WorldWideScience

Sample records for valence band offsets

  1. The Synthesis of NiO/TiO2 Heterostructures and Their Valence Band Offset Determination

    Directory of Open Access Journals (Sweden)

    Z. H. Ibupoto

    2014-01-01

    Full Text Available In this work, a heterojunction based on p-type NiO/n-type TiO2 nanostructures has been prepared on the fluorine doped tin oxide (FTO glass substrate by hydrothermal method. Scanning electron microscopy (SEM and X-Ray diffraction techniques were used for the morphological and crystalline arrays characterization. The X-ray photoelectron spectroscopy was employed to determine the valence-band offset (VBO of the NiO/TiO2 heterojunction prepared on FTO glass substrate. The core levels of Ni 2p and Ti 2p were utilized to align the valence-band offset of p-type NiO/n-type TiO2 heterojunction. The valence band offset was found to be ∼0.41 eV and the conduction band was calculated about ∼0.91 eV. The ratio of conduction band offset and the valence-band offset was found to be 2.21.

  2. Determination of a natural valence-band offset - The case of HgTe and CdTe

    Science.gov (United States)

    Shih, C. K.; Spicer, W. E.

    1987-01-01

    A method to determine a natural valence-band offset (NVBO), i.e., the change in the valence-band maximum energy which is intrinsic to the bulk band structures of semiconductors is proposed. The HgTe-CdTe system is used as an example in which it is found that the valence-band maximum of HgTe lies 0.35 + or - 0.06 eV above that of CdTe. The NVBO of 0.35 eV is in good agreement with the X-ray photoemission spectroscopy measurement of the heterojunction offset. The procedure to determine the NVBO between semiconductors, and its implication on the heterojunction band lineup and the electronic structures of semiconductor alloys, are discussed.

  3. Valence band offset of wurtzite InN/SrTiO3 heterojunction measured by x-ray photoelectron spectroscopy

    Directory of Open Access Journals (Sweden)

    Li Zhiwei

    2011-01-01

    Full Text Available Abstract The valence band offset (VBO of wurtzite indium nitride/strontium titanate (InN/SrTiO3 heterojunction has been directly measured by x-ray photoelectron spectroscopy. The VBO is determined to be 1.26 ± 0.23 eV and the conduction band offset is deduced to be 1.30 ± 0.23 eV, indicating the heterojunction has a type-I band alignment. The accurate determination of the valence and conduction band offsets paves a way to the applications of integrating InN with the functional oxide SrTiO3.

  4. Characterization of MBE-grown InAlN/GaN heterostructure valence band offsets with varying In composition

    Energy Technology Data Exchange (ETDEWEB)

    Jiao, Wenyuan, E-mail: wyjiaonju@gmail.com; Kong, Wei; Li, Jincheng; Kim, Tong-Ho; Brown, April S. [Department of Electrical and Computer Engineering, Duke University, Durham, NC, 27708 (United States); Collar, Kristen [Department of Physics, Duke University, Durham, NC, 27708 (United States); Losurdo, Maria [CNR-NANOTEC, Istituto di Nanotecnologia, via Orabona, 4-70126 Bari (Italy)

    2016-03-15

    Angle-resolved X-ray photoelectron spectroscopy (XPS) is used in this work to experimentally determine the valence band offsets of molecular beam epitaxy (MBE)-grown InAlN/GaN heterostructures with varying indium composition. We find that the internal electric field resulting from polarization must be taken into account when analyzing the XPS data. Valence band offsets of 0.12 eV for In{sub 0.18}Al{sub 0.82}N, 0.15 eV for In{sub 0.17}Al{sub 0.83}N, and 0.23 eV for In{sub 0.098}Al{sub 0.902}N with GaN are obtained. The results show that a compositional-depended bowing parameter is needed in order to estimate the valence band energies of InAlN as a function of composition in relation to those of the binary endpoints, AlN and InN.

  5. Characterization of MBE-grown InAlN/GaN heterostructure valence band offsets with varying In composition

    Directory of Open Access Journals (Sweden)

    Wenyuan Jiao

    2016-03-01

    Full Text Available Angle-resolved X-ray photoelectron spectroscopy (XPS is used in this work to experimentally determine the valence band offsets of molecular beam epitaxy (MBE-grown InAlN/GaN heterostructures with varying indium composition. We find that the internal electric field resulting from polarization must be taken into account when analyzing the XPS data. Valence band offsets of 0.12 eV for In0.18Al0.82N, 0.15 eV for In0.17Al0.83N, and 0.23 eV for In0.098Al0.902N with GaN are obtained. The results show that a compositional-depended bowing parameter is needed in order to estimate the valence band energies of InAlN as a function of composition in relation to those of the binary endpoints, AlN and InN.

  6. Valence band offset of β-Ga2O3/wurtzite GaN heterostructure measured by X-ray photoelectron spectroscopy.

    Science.gov (United States)

    Wei, Wei; Qin, Zhixin; Fan, Shunfei; Li, Zhiwei; Shi, Kai; Zhu, Qinsheng; Zhang, Guoyi

    2012-10-10

    A sample of the β-Ga2O3/wurtzite GaN heterostructure has been grown by dry thermal oxidation of GaN on a sapphire substrate. X-ray diffraction measurements show that the β-Ga2O3 layer was formed epitaxially on GaN. The valence band offset of the β-Ga2O3/wurtzite GaN heterostructure is measured by X-ray photoelectron spectroscopy. It is demonstrated that the valence band of the β-Ga2O3/GaN structure is 1.40 ± 0.08 eV.

  7. Measurement of the valence band-offset in a PbSe/ZnO heterojunction by x-ray photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Li Lin; Qiu Jijun; Weng Binbin; Yuan Zijian; Shi Zhisheng [School of Electrical and Computer Engineering, University of Oklahoma, Norman, Oklahoma 73019 (United States); Li Xiaomin; Gan Xiaoyan [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Sellers, Ian R. [Deparment of Physics, University of Oklahoma, Norman, Oklahoma 73019 (United States)

    2012-12-24

    A heterojunction of PbSe/ZnO has been grown by molecular beam epitaxy. X-ray photoelectron spectroscopy was used to directly measure the valence-band offset (VBO) of the heterojunction. The VBO, {Delta}E{sub V}, was determined as 2.51 {+-} 0.05 eV using the Pb 4p{sup 3/2} and Zn 2p{sup 3/2} core levels as a reference. The conduction-band offset, {Delta}E{sub C}, was, therefore, determined to be 0.59 {+-} 0.05 eV based on the above {Delta}E{sub V} value. This analysis indicates that the PbSe/ZnO heterojunction forms a type I (Straddling Gap) heterostructure.

  8. Valence and conduction band offsets at low-k a-SiO{sub x}C{sub y}:H/a-SiC{sub x}N{sub y}:H interfaces

    Energy Technology Data Exchange (ETDEWEB)

    King, Sean W., E-mail: sean.king@intel.com; Brockman, Justin; French, Marc; Jaehnig, Milt; Kuhn, Markus [Logic Technology Development, Intel Corporation, Hillsboro, Oregon 97124 (United States); French, Benjamin [Ocotillo Materials Laboratory, Intel Corporation, Chandler, Arizona 85248 (United States)

    2014-09-21

    In order to understand the fundamental electrical leakage and reliability failure mechanisms in nano-electronic low-k dielectric/metal interconnect structures, we have utilized x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy to determine the valence and conduction band offsets present at interfaces between non-porous and porous low-k a-SiO{sub x}C{sub y}:H interlayer dielectrics and a-SiC{sub x}N{sub y}:H metal capping layers. The valence band offset for such interfaces was determined to be 2.7±0.2 eV and weakly dependent on the a-SiOC:H porosity. The corresponding conduction band offset was determined to be 2.1±0.2 eV. The large band offsets indicate that intra metal layer leakage is likely dominated by defects and trap states in the a-SiOC:H and a-SiCN:H dielectrics.

  9. Band offsets in ITO/Ga2O3 heterostructures

    Science.gov (United States)

    Carey, Patrick H.; Ren, F.; Hays, David C.; Gila, B. P.; Pearton, S. J.; Jang, Soohwan; Kuramata, Akito

    2017-11-01

    The valence band offsets in rf-sputtered Indium Tin Oxide (ITO)/single crystal β-Ga2O3 (ITO/Ga2O3) heterostructures were measured with X-Ray Photoelectron Spectroscopy using the Kraut method. The bandgaps of the component materials in the heterostructure were determined by Reflection Electron Energy Loss Spectroscopy as 4.6 eV for Ga2O3 and 3.5 eV for ITO. The valence band offset was determined to be -0.78 ± 0.30 eV, while the conduction band offset was determined to be -0.32 ± 0.13 eV. The ITO/Ga2O3 system has a nested gap (type I) alignment. The use of a thin layer of ITO between a metal and the Ga2O3 is an attractive approach for reducing contact resistance on Ga2O3-based power electronic devices and solar-blind photodetectors.

  10. Band Offsets at the Interface between Crystalline and Amorphous Silicon from First Principles

    Science.gov (United States)

    Jarolimek, K.; Hazrati, E.; de Groot, R. A.; de Wijs, G. A.

    2017-07-01

    The band offsets between crystalline and hydrogenated amorphous silicon (a -Si ∶H ) are key parameters governing the charge transport in modern silicon heterojunction solar cells. They are an important input for macroscopic simulators that are used to further optimize the solar cell. Past experimental studies, using x-ray photoelectron spectroscopy (XPS) and capacitance-voltage measurements, have yielded conflicting results on the band offset. Here, we present a computational study on the band offsets. It is based on atomistic models and density-functional theory (DFT). The amorphous part of the interface is obtained by relatively long DFT first-principles molecular-dynamics runs at an elevated temperature on 30 statistically independent samples. In order to obtain a realistic conduction-band position the electronic structure of the interface is calculated with a hybrid functional. We find a slight asymmetry in the band offsets, where the offset in the valence band (0.29 eV) is larger than in the conduction band (0.17 eV). Our results are in agreement with the latest XPS measurements that report a valence-band offset of 0.3 eV [M. Liebhaber et al., Appl. Phys. Lett. 106, 031601 (2015), 10.1063/1.4906195].

  11. Valence and conduction band offsets of β-Ga2O3/AlN heterojunction

    Science.gov (United States)

    Sun, Haiding; Torres Castanedo, C. G.; Liu, Kaikai; Li, Kuang-Hui; Guo, Wenzhe; Lin, Ronghui; Liu, Xinwei; Li, Jingtao; Li, Xiaohang

    2017-10-01

    Both β-Ga2O3 and wurtzite AlN have wide bandgaps of 4.5-4.9 and 6.1 eV, respectively. We calculated the in-plane lattice mismatch between the (-201) plane of β-Ga2O3 and the (0002) plane of AlN, which was found to be 2.4%. This is the smallest mismatch between β-Ga2O3 and binary III-nitrides which is beneficial for the formation of a high quality β-Ga2O3/AlN heterojunction. However, the valence and conduction band offsets (VBO and CBO) at the β-Ga2O3/AlN heterojunction have not yet been identified. In this study, a very thin (less than 2 nm) β-Ga2O3 layer was deposited on an AlN/sapphire template to form the heterojunction by pulsed laser deposition. High-resolution X-ray photoelectron spectroscopy revealed the core-level (CL) binding energies of Ga 3d and Al 2p with respect to the valence band maximum in individual β-Ga2O3 and AlN layers, respectively. The separation between Ga 3d and Al 2p CLs at the β-Ga2O3/AlN interface was also measured. Eventually, the VBO was found to be -0.55 ± 0.05 eV. Consequently, a staggered-gap (type II) heterojunction with a CBO of -1.75 ± 0.05 eV was determined. The identification of the band alignment of the β-Ga2O3/AlN heterojunction could facilitate the design of optical and electronic devices based on these and related alloys.

  12. Ab-initio calculation of the valence-band offset at strained GaAs/InAs (001) heterojunction

    International Nuclear Information System (INIS)

    Tit, N.; Peressi, M.

    1993-06-01

    We present a self consistent pseudopotential calculation of the valence band offset (VBO) at GaAs/InAs (001) strained heterojunction, which is chose as an example of the isovalent polar with common-anion lattice mismatched heterojunctions. The effects of strain are studied by looking at the variation of the VBO versus the in plane lattice constant, which is imposed by the substrate. Our results show that the VBO can be tuned by about 0.17 eV going from GaAs to InAs substrates. Comparison of our work with the available experimental and theoretical results is also discussed. (author). 25 refs, 3 figs, 5 tabs

  13. Valence and conduction band offsets of β-Ga2O3/AlN heterojunction

    KAUST Repository

    Sun, Haiding

    2017-10-16

    Both β-Ga2O3 and wurtzite AlN have wide bandgaps of 4.5–4.9 and 6.1 eV, respectively. We calculated the in-plane lattice mismatch between the (−201) plane of β-Ga2O3 and the (0002) plane of AlN, which was found to be 2.4%. This is the smallest mismatch between β-Ga2O3 and binary III-nitrides which is beneficial for the formation of a high quality β-Ga2O3/AlN heterojunction. However, the valence and conduction band offsets (VBO and CBO) at the β-Ga2O3/AlN heterojunction have not yet been identified. In this study, a very thin (less than 2 nm) β-Ga2O3 layer was deposited on an AlN/sapphire template to form the heterojunction by pulsed laser deposition. High-resolution X-ray photoelectron spectroscopy revealed the core-level (CL) binding energies of Ga 3d and Al 2p with respect to the valence band maximum in individual β-Ga2O3 and AlN layers, respectively. The separation between Ga 3d and Al 2p CLs at the β-Ga2O3/AlN interface was also measured. Eventually, the VBO was found to be −0.55 ± 0.05 eV. Consequently, a staggered-gap (type II) heterojunction with a CBO of −1.75 ± 0.05 eV was determined. The identification of the band alignment of the β-Ga2O3/AlN heterojunction could facilitate the design of optical and electronic devices based on these and related alloys.

  14. Determination of band offsets at strained NiO and MgO heterojunction for MgO as an interlayer in heterojunction light emitting diode applications

    Energy Technology Data Exchange (ETDEWEB)

    Singh, S.D., E-mail: devsh@rrcat.gov.in [Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013 (India); Nand, Mangla [Bhabha Atomic Research Centre, Mumbai, Maharashtra 400085 (India); Ajimsha, R.S.; Upadhyay, Anuj; Kamparath, Rajiv; Mukherjee, C.; Misra, P.; Sinha, A.K. [Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013 (India); Jha, S.N. [Bhabha Atomic Research Centre, Mumbai, Maharashtra 400085 (India); Ganguli, Tapas [Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013 (India)

    2016-12-15

    Highlights: • Valence band offset at NiO/MgO heterojunction is experimentally determined. • Experimentally determined value of 2.3 ± 0.4 eV is significantly larger than the predicted from theoretical calculations. • The value of valence band offset is in corroboration with that estimated from the band transitivity model. • Our result can be used to predict accurately carrier transport and electroluminescence mechanisms for heterojunction LEDs. - Abstract: Valence band offset of 2.3 ± 0.4 eV at strained NiO/MgO heterojunction is determined from photoelectron spectroscopy (PES) measurements. The determined value of valence band offset is larger than that is predicted from first principle calculations, but is in corroboration with that obtained from band transitivity rule. Our PES result indicates a larger value of the valence band offset at strained NiO/MgO heterojunction and can be used to predict accurately carrier transport and electroluminescence mechanisms for n-ZnO/MgO/p-NiO and p-NiO/MgO/n-GaN heterojunction light emitting diodes.

  15. Band offsets in HfTiO/InGaZnO4 heterojunction determined by X-ray photoelectron spectroscopy

    International Nuclear Information System (INIS)

    He, G.; Chen, X.F.; Lv, J.G.; Fang, Z.B.; Liu, Y.M.; Zhu, K.R.; Sun, Z.Q.; Liu, M.

    2015-01-01

    Highlights: • Band offsets in HfTiO/InGaZnO 4 heterojunction were determined by XPS. • Valence band offset of HfTiO/IGZO heterojunction is determined to be 0.35 eV. • Conduction band offset of 1.61 eV is deduced for HfTiO/IGZO heterojunction. - Abstract: In current report, X-ray photoelectron spectroscopy has been pursued to obtain the valence band discontinuity (ΔE v ) of sputter deposited HfTiO/InZnGaO 4 (IGZO) heterostructures. A ΔE v value of 0.32 ± 0.1 eV was obtained by using the Ga 2p3/2, Zn 2p3/2, and In 3d5/2 energy levels as references. Taking into consideration the experimental band gaps of 5.35 eV and 3.39 eV for HfTiO and IGZO thin films measured by absorption method, respectively, this would result in a conduction band offset of 1.64 eV in this heterostructure

  16. Band offsets in HfTiO/InGaZnO{sub 4} heterojunction determined by X-ray photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    He, G., E-mail: ganghe01@issp.ac.cn [School of Physics and Materials Science, Radiation Detection Materials & Devices Lab, Anhui University, Hefei 230601 (China); Chen, X.F. [School of Physics and Materials Science, Radiation Detection Materials & Devices Lab, Anhui University, Hefei 230601 (China); Lv, J.G., E-mail: jglv@hftc.edu.cn [School of Electronic and Information Engineering, Hefei Normal University, Hefei 230601 (China); Fang, Z.B., E-mail: csfzb@usx.edu.cn [Department of Physics, Shaoxing University, Shaoxing 312000 (China); Liu, Y.M.; Zhu, K.R.; Sun, Z.Q. [School of Physics and Materials Science, Radiation Detection Materials & Devices Lab, Anhui University, Hefei 230601 (China); Liu, M., E-mail: mliu@issp.ac.cn [Key Laboratory of Materials Physics, Anhui Key Laboratory of Nanomaterials and Nanostructure, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China)

    2015-09-05

    Highlights: • Band offsets in HfTiO/InGaZnO{sub 4} heterojunction were determined by XPS. • Valence band offset of HfTiO/IGZO heterojunction is determined to be 0.35 eV. • Conduction band offset of 1.61 eV is deduced for HfTiO/IGZO heterojunction. - Abstract: In current report, X-ray photoelectron spectroscopy has been pursued to obtain the valence band discontinuity (ΔE{sub v}) of sputter deposited HfTiO/InZnGaO{sub 4} (IGZO) heterostructures. A ΔE{sub v} value of 0.32 ± 0.1 eV was obtained by using the Ga 2p3/2, Zn 2p3/2, and In 3d5/2 energy levels as references. Taking into consideration the experimental band gaps of 5.35 eV and 3.39 eV for HfTiO and IGZO thin films measured by absorption method, respectively, this would result in a conduction band offset of 1.64 eV in this heterostructure.

  17. Pulsed laser deposition of HfO{sub 2} thin films on indium zinc oxide: Band offsets measurements

    Energy Technology Data Exchange (ETDEWEB)

    Craciun, D.; Craciun, V., E-mail: valentin.craciun@inflpr.ro

    2017-04-01

    Highlights: • High quality amorphous IZO and HfO{sub 2} films were obtained by PLD technique. • XPS measurements were used to obtain the valence band alignment in HfO{sub 2}/IZO heterostructure. • A valence band offset (ΔE{sub V}) of 1.75 eV was obtained for the HfO{sub 2}/IZO heterostructure. • A conduction band offset (ΔE{sub C}) of 0.65 eV was estimated for the HfO{sub 2}/IZO heterostructure. - Abstract: One of the most used dielectric films for amorphous indium zinc oxide (IZO) based thin films transistor is HfO{sub 2}. The estimation of the valence band discontinuity (ΔE{sub V}) of HfO{sub 2}/IZO heterostructure grown using the pulsed laser deposition technique, with In/(In + Zn) = 0.79, was obtained from X-ray photoelectron spectroscopy (XPS) measurements. The binding energies of Hf 4d5, Zn 2p3 and In 3d5 core levels and valence band maxima were measured for thick pure films and for a very thin HfO{sub 2} film deposited on a thick IZO film. A value of ΔE{sub V} = 1.75 ± 0.05 eV was estimated for the heterostructure. Taking into account the measured HfO{sub 2} and IZO optical bandgap values of 5.50 eV and 3.10 eV, respectively, a conduction band offset ΔE{sub C} = 0.65 ± 0.05 eV in HfO{sub 2}/IZO heterostructure was then obtained.

  18. Determination of the valence-band offset of CdS/CIS solar cell devices by target factor analysis

    Energy Technology Data Exchange (ETDEWEB)

    Niles, D.W.; Contreras, M.; Ramanathan, K.; Noufi, R. [National Renewable Energy Lab., Golden, CO (United States)

    1996-05-01

    X-ray photoemission spectroscopy (XPS) is used to determine and compare the valence-band offsets ({Delta}E{sub v}) for CdS grown by chemical bath deposition on single-crystal and thin-film CuInSe{sub 2} (CIS). The thin-film CIS device was suitable for photovoltaic energy production. By sputtering through the CdS/CIS interface and reducing the depth profile with target factor analysis, the magnitude of {Delta}E{sub v} was determined to be {Delta}E{sub v} = 1.06 {+-} 0.15 eV for both the single-crystal and thin-film interfaces. This determination of {Delta}E{sub v} is about 0.25 eV larger than many previously reported estimations CdS grown by physical vapor deposition on CIS and helps explain the record performance of CdS/CIS photovoltaic devices.

  19. The carrier transport mechanism and band offset at the interface of ZnO/n-Si(111) heterojunction

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yapeng, E-mail: liyp1984@126.com [School of Materials Science and Engineering, Shaanxi University of Technology, Hanzhong 723001 (China); Li, Yingfeng [School of Electrical Engineering, Shaanxi University of Technology, Hanzhong 723001 (China); Wang, Jianyuan [School of Nature and Applied Science, Northwestern Polytechnical University, Xi' an 710072 (China); He, Zhirong; Zhang, Yonghong; Yu, Qi; Hou, Juncai [School of Materials Science and Engineering, Shaanxi University of Technology, Hanzhong 723001 (China)

    2017-05-15

    Highlights: • The carrier transport deviated from ideal thermionic emission model. • One deep level present at the interface of ZnO/n-Si(111) heterojunction. • The band offsets of ZnO/n-Si(111) heterojunction are a type-II band alignment. - Abstract: The ZnO films were deposited on the surface of n-Si(111) substrate by pulsed laser deposition for fabrication of ZnO/n-Si(111) heterojunction. The carrier transport mechanism, deep level defects and band offsets at the interface of ZnO/n-Si(111) heterojunction were investigated by current- voltage measurement, deep level transient spectroscopy, X-ray photoelectron spectroscopy, respectively. The results showed that the barrier height and ideality factor values varied in the different linear voltage range by using the thermionic emission model, which was due to the deep level participated in carrier transport. Meanwhile, it was found that one deep level appeared at the interface of ZnO/n-Si(111) heterojunction with densities of the deep level about 8.5 × 10{sup 16} cm{sup −3} and activation energies about 224 m eV, which originated from O{sup 2−} vacancies of ZnO films. In addition, the valence band offset of the ZnO/n-Si(111) heterojunction can be calculated to be −2.4 ± 0.15 eV. The conduction band offset is deduced to be −3.5 ± 0.15 eV from the valence band offset value, indicating that the band offsets of ZnO/n-Si(111) heterojunction is a type-II band alignment.

  20. Measurement of core level and band offsets at the interface of ITO/Hg_3In_2Te_6(1 1 0) heterojunction by synchrotron radiation photoelectron spectroscopy

    International Nuclear Information System (INIS)

    Li, Yapeng; Fu, Li; Sun, Jie; Ibrahim, Kurash; Wang, Jia-ou

    2016-01-01

    Highlights: • The valence band maximum of ITO film and MIT were measured to be 1.6 eV and 0.6 eV, respectively. • The concentration of In element presented a trend of increasing first and then decreasing from MIT to ITO. • The valence band offsets of the ITO/MIT(1 1 0) heterojunction was confirmed to be a type-II band alignment phenomenon. - Abstract: The Indium Tin Oxide (ITO) film was deposited on the surface of Hg_3In_2Te_6 (short for MIT) (1 1 0) for the fabrication of ITO/MIT(1 1 0) heterojunction by using the pulsed laser deposition method. In situ X-ray photoelectron spectroscopy was utilized to examine the band offsets and core level of ITO/MIT(1 1 0) heterojunctions. The result showed that the valence band maximum of ITO films and MIT(1 1 0) were 1.6 eV and 0.6 eV, respectively. Meanwhile, it was found that the binding energy of Te 3d, Sn 3d and Hg 4f remained unchanged during the ITO deposition process. However, the binding energy of O 1s and In 3d_5_/_2 increased about 0.3 eV and 0.2 eV, respectively, with the thickness increasing of ITO film from 3.5 nm to 5 nm. This may due to the elements diffusion at the interface region during the film growing process. According to the core level spectrum, it can be speculated that no significant chemical reaction occurred at the interface of ITO/MIT(1 1 0). In addition, the valence band offset of the ITO/MIT(1 1 0) heterojunction can be calculated to be −1 ± 0.15 eV by the means of the photoelectron spectroscopy methods. The conduction band offset is deduced to be −3.96 ± 0.15 eV from the known valence band offset value, indicating that the band offsets of ITO/MIT(1 1 0) heterojunction is a type-II band alignment.

  1. Measurement of ZnO/Al2O3 Heterojunction Band Offsets by in situ X-Ray Photoelectron Spectroscopy

    International Nuclear Information System (INIS)

    Lei Hong-Wen; Zhang Hong; Wang Xue-Min; Zhao Yan; Yan Da-Wei; Jiang Zhong-Qian; Yao Gang; Zeng Ti-Xian; Wu Wei-Dong

    2013-01-01

    ZnO films are grown on c-sapphire substrates by laser molecular beam epitaxy. The band offsets of the ZnO/Al 2 O 3 heterojunction are studied by in situ x-ray photoelectron spectroscopy. The valence band of Al 2 O 3 is found to be 3.59±0.05eV below that of ZnO. Together with the resulting conduction band offset of 2.04±0.05eV, this indicates that a type-I staggered band line exists at the ZnO/Al 2 O 3 heterojunction

  2. Determination of band offsets at GaN/single-layer MoS2 heterojunction

    KAUST Repository

    Tangi, Malleswararao

    2016-07-25

    We report the band alignment parameters of the GaN/single-layer (SL) MoS2 heterostructure where the GaN thin layer is grown by molecular beam epitaxy on CVD deposited SL-MoS2/c-sapphire. We confirm that the MoS2 is an SL by measuring the separation and position of room temperature micro-Raman E1 2g and A1 g modes, absorbance, and micro-photoluminescence bandgap studies. This is in good agreement with HRTEM cross-sectional analysis. The determination of band offset parameters at the GaN/SL-MoS2 heterojunction is carried out by high-resolution X-ray photoelectron spectroscopy accompanying with electronic bandgap values of SL-MoS2 and GaN. The valence band and conduction band offset values are, respectively, measured to be 1.86 ± 0.08 and 0.56 ± 0.1 eV with type II band alignment. The determination of these unprecedented band offset parameters opens up a way to integrate 3D group III nitride materials with 2D transition metal dichalcogenide layers for designing and modeling of their heterojunction based electronic and photonic devices.

  3. Determination of band offsets at GaN/single-layer MoS2 heterojunction

    KAUST Repository

    Tangi, Malleswararao; Mishra, Pawan; Ng, Tien Khee; Hedhili, Mohamed N.; Janjua, Bilal; Alias, Mohd Sharizal; Anjum, Dalaver H.; Tseng, Chien-Chih; Shi, Yumeng; Joyce, Hannah J.; Li, Lain-Jong; Ooi, Boon S.

    2016-01-01

    We report the band alignment parameters of the GaN/single-layer (SL) MoS2 heterostructure where the GaN thin layer is grown by molecular beam epitaxy on CVD deposited SL-MoS2/c-sapphire. We confirm that the MoS2 is an SL by measuring the separation and position of room temperature micro-Raman E1 2g and A1 g modes, absorbance, and micro-photoluminescence bandgap studies. This is in good agreement with HRTEM cross-sectional analysis. The determination of band offset parameters at the GaN/SL-MoS2 heterojunction is carried out by high-resolution X-ray photoelectron spectroscopy accompanying with electronic bandgap values of SL-MoS2 and GaN. The valence band and conduction band offset values are, respectively, measured to be 1.86 ± 0.08 and 0.56 ± 0.1 eV with type II band alignment. The determination of these unprecedented band offset parameters opens up a way to integrate 3D group III nitride materials with 2D transition metal dichalcogenide layers for designing and modeling of their heterojunction based electronic and photonic devices.

  4. Band offsets of non-polar A-plane GaN/AlN and AlN/GaN heterostructures measured by X-ray photoemission spectroscopy.

    Science.gov (United States)

    Sang, Ling; Zhu, Qin Sheng; Yang, Shao Yan; Liu, Gui Peng; Li, Hui Jie; Wei, Hong Yuan; Jiao, Chun Mei; Liu, Shu Man; Wang, Zhan Guo; Zhou, Xiao Wei; Mao, Wei; Hao, Yue; Shen, Bo

    2014-01-01

    The band offsets of non-polar A-plane GaN/AlN and AlN/GaN heterojunctions are measured by X-ray photoemission spectroscopy. A large forward-backward asymmetry is observed in the non-polar GaN/AlN and AlN/GaN heterojunctions. The valence-band offsets in the non-polar A-plane GaN/AlN and AlN/GaN heterojunctions are determined to be 1.33 ± 0.16 and 0.73 ± 0.16 eV, respectively. The large valence-band offset difference of 0.6 eV between the non-polar GaN/AlN and AlN/GaN heterojunctions is considered to be due to piezoelectric strain effect in the non-polar heterojunction overlayers.

  5. Asymmetric band offsets in silicon heterojunction solar cells: Impact on device performance

    Energy Technology Data Exchange (ETDEWEB)

    Seif, Johannes Peter, E-mail: johannes.seif@alumni.epfl.ch; Ballif, Christophe; De Wolf, Stefaan [Photovoltaics and Thin-Film Electronics Laboratory, Institute of Microengineering (IMT), Ecole Polytechnique Fédérale de Lausanne (EPFL), Rue de la Maladière 71b, CH-2002 Neuchâtel (Switzerland); Menda, Deneb; Özdemir, Orhan [Department of Physics, Yıldız Technical University, Davutpasa Campus, TR-34210 Esenler, Istanbul (Turkey); Descoeudres, Antoine; Barraud, Loris [CSEM, PV-Center, Jaquet-Droz 1, CH-2002 Neuchâtel (Switzerland)

    2016-08-07

    Amorphous/crystalline silicon interfaces feature considerably larger valence than conduction band offsets. In this article, we analyze the impact of such band offset asymmetry on the performance of silicon heterojunction solar cells. To this end, we use silicon suboxides as passivation layers—inserted between substrate and (front or rear) contacts—since such layers enable intentionally exacerbated band-offset asymmetry. Investigating all topologically possible passivation layer permutations and focussing on light and dark current-voltage characteristics, we confirm that to avoid fill factor losses, wider-bandgap silicon oxide films (of at least several nanometer thin) should be avoided in hole-collecting contacts. As a consequence, device implementation of such films as window layers—without degraded carrier collection—demands electron collection at the front and hole collection at the rear. Furthermore, at elevated operating temperatures, once possible carrier transport barriers are overcome by thermionic (field) emission, the device performance is mainly dictated by the passivation of its surfaces. In this context, compared to the standard amorphous silicon layers, the wide-bandgap oxide layers applied here passivate remarkably better at these temperatures, which may represent an additional benefit under practical operation conditions.

  6. Determination of band offsets at GaN/single-layer MoS{sub 2} heterojunction

    Energy Technology Data Exchange (ETDEWEB)

    Tangi, Malleswararao; Mishra, Pawan; Ng, Tien Khee; Janjua, Bilal; Alias, Mohd Sharizal; Ooi, Boon S., E-mail: boon.ooi@kaust.edu.sa [Photonics Laboratory, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900 (Saudi Arabia); Hedhili, Mohamed Nejib; Anjum, Dalaver H. [Adavanced Nanofabrication Imaging and Characterization, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900 (Saudi Arabia); Tseng, Chien-Chih; Shi, Yumeng; Li, Lain-Jong [Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900 (Saudi Arabia); Joyce, Hannah J. [Department of Engineering, University of Cambridge, 9 JJ Thomson Avenue, Cambridge, Cambridgeshire CB3 0FA (United Kingdom)

    2016-07-18

    We report the band alignment parameters of the GaN/single-layer (SL) MoS{sub 2} heterostructure where the GaN thin layer is grown by molecular beam epitaxy on CVD deposited SL-MoS{sub 2}/c-sapphire. We confirm that the MoS{sub 2} is an SL by measuring the separation and position of room temperature micro-Raman E{sup 1}{sub 2g} and A{sup 1}{sub g} modes, absorbance, and micro-photoluminescence bandgap studies. This is in good agreement with HRTEM cross-sectional analysis. The determination of band offset parameters at the GaN/SL-MoS{sub 2} heterojunction is carried out by high-resolution X-ray photoelectron spectroscopy accompanying with electronic bandgap values of SL-MoS{sub 2} and GaN. The valence band and conduction band offset values are, respectively, measured to be 1.86 ± 0.08 and 0.56 ± 0.1 eV with type II band alignment. The determination of these unprecedented band offset parameters opens up a way to integrate 3D group III nitride materials with 2D transition metal dichalcogenide layers for designing and modeling of their heterojunction based electronic and photonic devices.

  7. Band offsets of novel CoTiO{sub 3}/Ag{sub 3}VO{sub 4} heterojunction measured by X-ray photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Wangkawong, Kanlayawat [Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200 (Thailand); Tantraviwat, Doldet [Thai Microelectronics Center (TMEC), National Electronics and Computer Technology Center (NECTEC), Chachoengsao 24000 (Thailand); Phanichphant, Sukon [Materials Science Research Centre, Faculty of Science, Chiang Mai University, Chiang Mai 50200 (Thailand); Inceesungvorn, Burapat, E-mail: binceesungvorn@gmail.com [Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200 (Thailand)

    2015-01-01

    Highlights: • Band lineup of novel CoTiO{sub 3}/Ag{sub 3}VO{sub 4} composite is determined by semidirect XPS method. • The composite forms a type-II staggered heterojunction. • Valence and conduction-band offsets are 0.2 ± 0.3 and −0.6 ± 0.3 eV, respectively. • Band lineup determination is needed for understanding charge transfer at interfaces. - Abstract: The energy band diagram and band offsets of the novel CoTiO{sub 3}/Ag{sub 3}VO{sub 4} heterojunction photocatalyst are investigated by X-ray photoelectron spectroscopy for the first time. Excluding the strain effect, the valence-band and conduction-band offsets are determined to be 0.2 ± 0.3 eV and −0.6 ± 0.3 eV, respectively. The CoTiO{sub 3}/Ag{sub 3}VO{sub 4} composite forms a type-II heterojunction, for which the photogenerated charge carriers could be effectively separated. The results suggest that determination of the energy band structure is crucial for understanding the photogenerated charge transfer mechanism at the interfaces, hence the corresponding photocatalytic activity and would also be beneficial to the design of new and efficient heterostructure-based photocatalysts.

  8. Electron and hole photoemission detection for band offset determination of tunnel field-effect transistor heterojunctions

    International Nuclear Information System (INIS)

    Li, Wei; Zhang, Qin; Kirillov, Oleg A.; Levin, Igor; Richter, Curt A.; Gundlach, David J.; Nguyen, N. V.; Bijesh, R.; Datta, S.; Liang, Yiran; Peng, Lian-Mao; Liang, Xuelei

    2014-01-01

    We report experimental methods to ascertain a complete energy band alignment of a broken-gap tunnel field-effect transistor based on an InAs/GaSb hetero-junction. By using graphene as an optically transparent electrode, both the electron and hole barrier heights at the InAs/GaSb interface can be quantified. For a Al 2 O 3 /InAs/GaSb layer structure, the barrier height from the top of the InAs and GaSb valence bands to the bottom of the Al 2 O 3 conduction band is inferred from electron emission whereas hole emissions reveal the barrier height from the top of the Al 2 O 3 valence band to the bottom of the InAs and GaSb conduction bands. Subsequently, the offset parameter at the broken gap InAs/GaSb interface is extracted and thus can be used to facilitate the development of predicted models of electron quantum tunneling efficiency and transistor performance

  9. Measurement of core level and band offsets at the interface of ITO/Hg{sub 3}In{sub 2}Te{sub 6}(1 1 0) heterojunction by synchrotron radiation photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yapeng [State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an 710072 (China); Fu, Li, E-mail: fuli@nwpu.edu.cn [State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an 710072 (China); Sun, Jie [State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an 710072 (China); Ibrahim, Kurash; Wang, Jia-ou [Laboratory of Synchrotron Radiation, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039 (China)

    2016-02-15

    Highlights: • The valence band maximum of ITO film and MIT were measured to be 1.6 eV and 0.6 eV, respectively. • The concentration of In element presented a trend of increasing first and then decreasing from MIT to ITO. • The valence band offsets of the ITO/MIT(1 1 0) heterojunction was confirmed to be a type-II band alignment phenomenon. - Abstract: The Indium Tin Oxide (ITO) film was deposited on the surface of Hg{sub 3}In{sub 2}Te{sub 6} (short for MIT) (1 1 0) for the fabrication of ITO/MIT(1 1 0) heterojunction by using the pulsed laser deposition method. In situ X-ray photoelectron spectroscopy was utilized to examine the band offsets and core level of ITO/MIT(1 1 0) heterojunctions. The result showed that the valence band maximum of ITO films and MIT(1 1 0) were 1.6 eV and 0.6 eV, respectively. Meanwhile, it was found that the binding energy of Te 3d, Sn 3d and Hg 4f remained unchanged during the ITO deposition process. However, the binding energy of O 1s and In 3d{sub 5/2} increased about 0.3 eV and 0.2 eV, respectively, with the thickness increasing of ITO film from 3.5 nm to 5 nm. This may due to the elements diffusion at the interface region during the film growing process. According to the core level spectrum, it can be speculated that no significant chemical reaction occurred at the interface of ITO/MIT(1 1 0). In addition, the valence band offset of the ITO/MIT(1 1 0) heterojunction can be calculated to be −1 ± 0.15 eV by the means of the photoelectron spectroscopy methods. The conduction band offset is deduced to be −3.96 ± 0.15 eV from the known valence band offset value, indicating that the band offsets of ITO/MIT(1 1 0) heterojunction is a type-II band alignment.

  10. Study of interfaces and band offsets in TiN/amorphous LaLuO3 gate stacks

    KAUST Repository

    Mitrovic, Ivona Z.

    2011-07-01

    TiN/LaLuO3 (LLO) gate stacks formed by molecular beam deposition have been investigated by X-ray photoelectron spectroscopy, medium energy ion scattering, spectroscopic ellipsometry, scanning transmission electron microscopy, electron energy loss spectroscopy and atomic force microscopy. The results indicate an amorphous structure for deposited LLO films. The band offset between the Fermi level of TiN and valence band of LLO is estimated to be 2.65 ± 0.05 eV. A weaker La-O-Lu bond and a prominent Ti2p sub-peak which relates to Ti bond to interstitial oxygen have been identified for an ultra-thin 1.7 nm TiN/3 nm LLO gate stack. The angle-dependent XPS analysis of Si2s spectra as well as shifts of La4d, La3d and Lu4d core levels suggests a silicate-type with Si-rich SiOx LLO/Si interface. Symmetrical valence and conduction band offsets for LLO to Si of 2.2 eV and the bandgap of 5.5 ± 0.1 eV have been derived from the measurements. The band alignment for ultra-thin TiN/LLO gate stack is affected by structural changes. Copyright © 2011 Published by Elsevier B.V. All rights reserved.

  11. Band offsets and electronic structures of interface between In{sub 0.5}Ga{sub 0.5}As and InP

    Energy Technology Data Exchange (ETDEWEB)

    Cai, Genwang [School of Physical Science and Engineering and Key Laboratory of Materials Physics of Ministry of Education of China, Zhengzhou University, Zhengzhou 450052 (China); College of Science, Henan University of Technology, Zhengzhou 450001 (China); Wang, Changhong; Wang, Weichao [College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300071 (China); Liang, Erjun, E-mail: ejliang@zzu.edu.cn [School of Physical Science and Engineering and Key Laboratory of Materials Physics of Ministry of Education of China, Zhengzhou University, Zhengzhou 450052 (China)

    2016-02-07

    III–V semiconductor interfacing with high-κ gate oxide is crucial for the high mobility metal-oxide-semiconductor field transistor device. With density functional theory calculations, we explored the band offsets and electronic structures of the In{sub 0.5}Ga{sub 0.5}As/InP interfaces with various interfacial bondings. Among six different bonding interfaces, we found that P-In(Ga) bonding interface showed the highest stability. Local density of states calculations was adopted to calculate the band offsets. Except for the metallic interface, we noticed that neither valence band offset nor conduction band offset depended on the interfacial bondings. For the most stable P-In(Ga) interface, we did not observe any gap states. Furthermore, we explored the P-In(Ga) interfaces with interfacial P-As exchange defects, which slightly modified the interface stability and the band offsets but did not produce any gap states. These findings provide solid evidence that InP could serve as a promising interfacial passivation layer between III–V material and high-κ oxide in the application of high mobility devices.

  12. Hole energy and momentum distributions in valence bands

    International Nuclear Information System (INIS)

    Laan, G. van der.

    1982-01-01

    In order to understand the electrical and magnetic properties of solids, the knowledge of the density of states and the dispersion relation of the valence bands is indispensable. This thesis offers some alternative methods to obtain information about the nature of the valence band. Part A deals with the energy distribution of the photoelectrons. A simple model, which explains the core hole satellite structure in compounds with large correlation effects between the valence band holes and the created photo-hole, is outlined. CuCl, CuX 2 (X = F Cl and Br) are studied, by photoemission and Auger electron spectroscopies in determining the valence band properties. Part B deals with the simultaneous measurement of the energy and the wave vector of the emitted electrons. A practical example is given for the determination of the dispersion relation in copper. The measurements of a surface resonance band and the distribution of the secondary electrons are also reported. (Auth.)

  13. Modification of band offsets of InGaZnO4/Si heterojunction through nitrogenation treatment

    International Nuclear Information System (INIS)

    Chen, X.F.; He, G.; Lv, J.G.; Liu, M.; Wang, P.H.; Chen, X.S.; Sun, Z.Q.

    2015-01-01

    The effect of nitrogen on the band offset of sputtering-derived InZnGaO 4 (IGZO)/Si heterostructures has been systematically investigated by x-ray photoelectron spectroscopy (XPS) measurements. Elemental analysis indicates that nitrogen has been successfully incorporated into the IGZO film. By using In 3d 5/2 , In 3d 3/2 and Ga 3d core level (CL) XPS spectra as references, values of valence band offsets (ΔE v ) of have been determined to be 2.56 ± 0.02 and 2.44 ± 0.02 eV for IGZO/Si and IGZO:N/Si heterojunctions, respectively. Using the experimental band gap of 3.59 and 3.50 eV of the IGZO/Si and IGZO:N/Si, the calculated values of conduction band offset (ΔE c ) is 0.09 ± 0.01 and 0.06 ± 0.01 eV, respectively. The results indicate that nitrogen incorporation leads to the reduction in band gap and ΔE v and the slight effect on the ΔE c has also been detected. - Highlights: • α-IGZO/Si and α-IGZO:N/Si heterostructures have been obtained by sputtering. • Nitrogen dependent ΔE v and ΔE v have been determined by XPS measurements. • Nitrogen incorporation in IGZO leads to the reduced band gap and increased ΔE v . • Nitrogen incorporation has no apparent effect on the ΔE c of α-IGZO/Si

  14. X-ray photoelectron spectroscopy investigations of band offsets in Ga0.02Zn0.98O/ZnO heterojunction for UV photodetectors

    Science.gov (United States)

    Singh, Karmvir; Rawal, Ishpal; Punia, Rajesh; Dhar, Rakesh

    2017-10-01

    Here, we report the valence and conduction band offset measurements in pure ZnO and the Ga0.02Zn0.98O/ZnO heterojunction by X-Ray photoelectron spectroscopy studies for UV photodetector applications. For detailed investigations on the band offsets and UV photodetection behavior of Ga0.02Zn0.98O/ZnO heterostructures, thin films of pristine ZnO, Ga-doped ZnO (Ga0.02Zn0.98O), and heterostructures of Ga-doped ZnO with ZnO (Ga0.02Zn0.98O/ZnO) were deposited using a pulsed laser deposition technique. The deposited thin films were characterized by X-ray diffraction, atomic force microscopy, and UV-Vis spectroscopy. X-ray photoelectron spectroscopy studies were carried out on all the thin films for the investigation of valence and conduction band offsets. The valence band was found to be shifted by 0.28 eV, while the conduction band has a shifting of -0.272 eV in the Ga0.02Zn0.98O/ZnO heterojunction as compared to pristine ZnO thin films. All the three samples were analyzed for photoconduction behavior under UVA light of the intensity of 3.3 mW/cm2, and it was observed that the photoresponse of pristine ZnO (19.75%) was found to increase with 2 wt. % doping of Ga (22.62%) and heterostructured thin films (29.10%). The mechanism of UV photodetection in the deposited samples has been discussed in detail, and the interaction of chemisorbed oxygen on the ZnO surface with holes generated by UV light exposure has been the observed mechanism for the change in electrical conductivity responsible for UV photoresponse on the present deposited ZnO films.

  15. Band offsets and growth mode of molecular beam epitaxy grown MgO (111) on GaN (0002) by x-ray photoelectron spectroscopy

    Science.gov (United States)

    Craft, H. S.; Collazo, R.; Losego, M. D.; Mita, S.; Sitar, Z.; Maria, J.-P.

    2007-10-01

    MgO is a proposed dielectric for use as a tunneling barrier in devices integrating GaN and ferroelectric oxides. In this study, we present data regarding the growth mode and band offsets of MgO grown epitaxially on GaN (0002) surfaces using molecular beam epitaxy. Using in situ x-ray photoelectron spectroscopy (XPS) and molecular beam epitaxy, we determine, from sequential growth experiments, that the growth of MgO proceeds via the Volmer-Weber (three-dimensional) mode, and full coalescence of the film does not occur until approximately 12nm of MgO has been deposited. The observation of a three-dimensional growth mode is in agreement with previously published data. For the valence band offset, we find a value of 1.2±0.2eV, which corresponds to a 3.2eV conduction band offset. XPS measurements suggest a chemically abrupt interface and no effect on band lineup due to the slow coalescence behavior.

  16. Band offsets and growth mode of molecular beam epitaxy grown MgO (111) on GaN (0002) by x-ray photoelectron spectroscopy

    International Nuclear Information System (INIS)

    Craft, H. S.; Collazo, R.; Losego, M. D.; Mita, S.; Sitar, Z.; Maria, J.-P.

    2007-01-01

    MgO is a proposed dielectric for use as a tunneling barrier in devices integrating GaN and ferroelectric oxides. In this study, we present data regarding the growth mode and band offsets of MgO grown epitaxially on GaN (0002) surfaces using molecular beam epitaxy. Using in situ x-ray photoelectron spectroscopy (XPS) and molecular beam epitaxy, we determine, from sequential growth experiments, that the growth of MgO proceeds via the Volmer-Weber (three-dimensional) mode, and full coalescence of the film does not occur until approximately 12 nm of MgO has been deposited. The observation of a three-dimensional growth mode is in agreement with previously published data. For the valence band offset, we find a value of 1.2±0.2 eV, which corresponds to a 3.2 eV conduction band offset. XPS measurements suggest a chemically abrupt interface and no effect on band lineup due to the slow coalescence behavior

  17. Theoretical and experimental studies of the ZnSe/CuInSe2 heterojunction band offset

    International Nuclear Information System (INIS)

    Nelson, A.J.; Schwerdtfeger, C.R.; Wei, S.; Zunger, A.; Rioux, D.; Patel, R.; Hoechst, H.

    1993-01-01

    We report first-principles band structure calculations that show that ZnSe/CuInSe 2 has a significant valence band offset (VBO, ΔE v ): 0.70±0.05 eV for the relaxed interface and 0.60±0.05 eV for the coherent interface. These large values demonstrate the failure of the common anion rule. This is traced to a stronger Cu,d-Se,p level repulsion in CuInSe 2 than the Zn,d-Se,p repulsion in ZnSe. The VBO was then studied by synchrotron radiation soft x-ray photoemission spectroscopy. ZnSe overlayers were sequentially grown in steps on n-type CuInSe 2 (112) single crystals at 200 degree C. In situ photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the In 4d and Zn 3d core lines. Results of these measurements reveal that the VBO is ΔE v =0.70±0.15 eV, in good agreement with the first-principles prediction

  18. Modification of band offsets of InGaZnO{sub 4}/Si heterojunction through nitrogenation treatment

    Energy Technology Data Exchange (ETDEWEB)

    Chen, X.F. [School of Physics and Materials Science, Radiation Detection Materials & Devices Lab, Anhui University, Hefei 230601 (China); He, G., E-mail: hegang@ahu.edu.cn [School of Physics and Materials Science, Radiation Detection Materials & Devices Lab, Anhui University, Hefei 230601 (China); National Laboratory for Infrared Physics, Chinese Academy of Sciences, Shanghai Institute of Technical Physics, 500 Yutian Road, Shanghai 200083 (China); Lv, J.G., E-mail: jglv@hftc.edu.cn [Department of Physics and Electronic Engineering, Hefei Normal University, Hefei 230061 (China); Liu, M., E-mail: mliu@issp.ac.cn [Key Laboratory of Materials Physics, Anhui Key Laboratory of Nanomaterials and Nanostructure, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Wang, P.H. [School of Physics and Materials Science, Radiation Detection Materials & Devices Lab, Anhui University, Hefei 230601 (China); Chen, X.S. [National Laboratory for Infrared Physics, Chinese Academy of Sciences, Shanghai Institute of Technical Physics, 500 Yutian Road, Shanghai 200083 (China); Sun, Z.Q. [School of Physics and Materials Science, Radiation Detection Materials & Devices Lab, Anhui University, Hefei 230601 (China)

    2015-10-25

    The effect of nitrogen on the band offset of sputtering-derived InZnGaO{sub 4} (IGZO)/Si heterostructures has been systematically investigated by x-ray photoelectron spectroscopy (XPS) measurements. Elemental analysis indicates that nitrogen has been successfully incorporated into the IGZO film. By using In 3d{sub 5/2}, In 3d{sub 3/2} and Ga 3d core level (CL) XPS spectra as references, values of valence band offsets (ΔE{sub v}) of have been determined to be 2.56 ± 0.02 and 2.44 ± 0.02 eV for IGZO/Si and IGZO:N/Si heterojunctions, respectively. Using the experimental band gap of 3.59 and 3.50 eV of the IGZO/Si and IGZO:N/Si, the calculated values of conduction band offset (ΔE{sub c}) is 0.09 ± 0.01 and 0.06 ± 0.01 eV, respectively. The results indicate that nitrogen incorporation leads to the reduction in band gap and ΔE{sub v} and the slight effect on the ΔE{sub c} has also been detected. - Highlights: • α-IGZO/Si and α-IGZO:N/Si heterostructures have been obtained by sputtering. • Nitrogen dependent ΔE{sub v} and ΔE{sub v} have been determined by XPS measurements. • Nitrogen incorporation in IGZO leads to the reduced band gap and increased ΔE{sub v}. • Nitrogen incorporation has no apparent effect on the ΔE{sub c} of α-IGZO/Si.

  19. Band structure, band offsets, substitutional doping, and Schottky barriers of bulk and monolayer InSe

    Science.gov (United States)

    Guo, Yuzheng; Robertson, John

    2017-09-01

    We present a detailed study of the electronic structure of the layered semiconductor InSe. We calculate the band structure of the monolayer and bulk material using density functional theory, hybrid functionals, and G W . The band gap of the monolayer InSe is calculated to be 2.4 eV in screened exchange hybrid functional, close to the experimental photoluminescence gap. The electron affinities and band offsets are calculated for vertical stacked-layer heterostructures, and are found to be suitable for tunnel field effect transistors (TFETs) in combination with WS e2 or similar. The valence-band edge of InSe is calculated to lie 5.2 eV below the vacuum level, similar to that for the closed shell systems HfS e2 or SnS e2 . Hence InSe would be suitable to act as a p -type drain in the TFET. The intrinsic defects are calculated. For Se-rich layers, the Se adatom (interstitial) is found to be the most stable defect, whereas for In-rich layers, the Se vacancy is the most stable for the neutral state. Antisites tend to have energies just above those of vacancies. The Se antisite distorts towards a bond-breaking distortion as in the EL2 center of GaAs. Both substitutional donors and acceptors are calculated to be shallow, and effective dopants. They do not reconstruct to form nondoping configurations as occurs in black phosphorus. Finally, the Schottky barriers of metals on InSe are found to be strongly pinned by metal induced gap states (MIGS) at ˜0.5 eV above the valence-band edge. Any interfacial defects would lead to a stronger pinning at a similar energy. Overall, InSe is an effective semiconductor combining the good features of 2D (lack of dangling bonds, etc.) with the good features of 3D (effective doping), which few others achieve.

  20. Valence band structure of binary chalcogenide vitreous semiconductors by high-resolution XPS

    International Nuclear Information System (INIS)

    Kozyukhin, S.; Golovchak, R.; Kovalskiy, A.; Shpotyuk, O.; Jain, H.

    2011-01-01

    High-resolution X-ray photoelectron spectroscopy (XPS) is used to study regularities in the formation of valence band electronic structure in binary As x Se 100−x , As x S 100−x , Ge x Se 100−x and Ge x S 100−x chalcogenide vitreous semiconductors. It is shown that the highest occupied energetic states in the valence band of these materials are formed by lone pair electrons of chalcogen atoms, which play dominant role in the formation of valence band electronic structure of chalcogen-rich glasses. A well-expressed contribution from chalcogen bonding p electrons and more deep s orbitals are also recorded in the experimental valence band XPS spectra. Compositional dependences of the observed bands are qualitatively analyzed from structural and compositional points of view.

  1. Valence band structure of binary chalcogenide vitreous semiconductors by high-resolution XPS

    Energy Technology Data Exchange (ETDEWEB)

    Kozyukhin, S., E-mail: sergkoz@igic.ras.ru [Russian Academy of Science, Institute of General and Inorganic Chemistry (Russian Federation); Golovchak, R. [Lviv Scientific Research Institute of Materials of SRC ' Carat' (Ukraine); Kovalskiy, A. [Lehigh University, Department of Materials Science and Engineering (United States); Shpotyuk, O. [Lviv Scientific Research Institute of Materials of SRC ' Carat' (Ukraine); Jain, H. [Lehigh University, Department of Materials Science and Engineering (United States)

    2011-04-15

    High-resolution X-ray photoelectron spectroscopy (XPS) is used to study regularities in the formation of valence band electronic structure in binary As{sub x}Se{sub 100-x}, As{sub x}S{sub 100-x}, Ge{sub x}Se{sub 100-x} and Ge{sub x}S{sub 100-x} chalcogenide vitreous semiconductors. It is shown that the highest occupied energetic states in the valence band of these materials are formed by lone pair electrons of chalcogen atoms, which play dominant role in the formation of valence band electronic structure of chalcogen-rich glasses. A well-expressed contribution from chalcogen bonding p electrons and more deep s orbitals are also recorded in the experimental valence band XPS spectra. Compositional dependences of the observed bands are qualitatively analyzed from structural and compositional points of view.

  2. Thickness-dependent change in the valence band offset of the SiO{sub 2}/Si interface studied using synchrotron-radiation photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Toyoda, S., E-mail: toyoda.satoshi.4w@kyoto-u.ac.jp; Oshima, M. [Department of Applied Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2016-08-28

    We have studied the thickness-dependent change in the valence band offset (VBO) of the SiO{sub 2}/Si(001) interface using synchrotron-radiation photoemission spectroscopy with soft and hard X-rays. The SiO{sub 2}-film thickness (T{sub ox}) and X-ray irradiation time (t{sub irrad}) were systematically parameterized to distinguish between the “intrinsic” T{sub ox} effects in the VBOs and the “extrinsic” differential charging phenomena in SiO{sub 2} films on Si substrates. The results revealed that at a spontaneous time (t{sub irrad} ≈ 5 s) that suppresses the differential charging phenomena as much as possible, the experimental VBO abruptly increases as a function of T{sub ox} and gradually saturates to the traditional VBO value range determined by the internal photoemission and photoconduction measurements. This effect is not attributed to the differential charging phenomena, but rather it is attributed to the “intrinsic” T{sub ox}-dependent change in the VBO. The two possible physical behaviors include electronic polarization and image charge. We have derived the electronic polarization contribution from experimental data by carefully describing the effects of the long-range image charges based on the classical dielectric-screening model.

  3. Measurement of valence band structure in arbitrary dielectric films

    International Nuclear Information System (INIS)

    Uhm, Han S.; Choi, Eun H.

    2012-01-01

    A new way of measuring the band structure of various dielectric materials using the secondary electron emission from Auger neutralization of ions is introduced. The first example of this measurement scheme is the magnesium oxide (MgO) films with respect to the application of the films in the display industries. The density of state in the valence bands of MgO film and MgO film with a functional layer (FL) deposited over a dielectric surface reveals that the density peak of film with a FL is considerably less than that of film, thereby indicating a better performance of MgO film with functional layer in display devices. The second example of the measurement is the boron-zinc oxide (BZO) films with respect to the application of the films to the development of solar cells. The measurement of density of state in BZO film suggests that a high concentration of boron impurity in BZO films may enhance the transition of electrons and holes through the band gap from the valence to the conduction band in zinc oxide crystals; thereby improving the conductivity of the film. Secondary electron emission by the Auger neutralization of ions is highly instrumental for the determination of the density of states in the valence band of dielectric materials.

  4. Band alignment of type I at (100ZnTe/PbSe interface

    Directory of Open Access Journals (Sweden)

    Igor Konovalov

    2016-06-01

    Full Text Available A junction of lattice-matched cubic semiconductors ZnTe and PbSe results in a band alignment of type I so that the narrow band gap of PbSe is completely within the wider band gap of ZnTe. The valence band offset of 0.27 eV was found, representing a minor barrier during injection of holes from PbSe into ZnTe. Simple linear extrapolation of the valence band edge results in a smaller calculated band offset, but a more elaborate square root approximation was used instead, which accounts for parabolic bands. PbSe was electrodeposited at room temperature with and without Cd2+ ions in the electrolyte. Although Cd adsorbs at the surface, the presence of Cd in the electrolyte does not influence the band offset.

  5. Interface termination and band alignment of epitaxially grown alumina films on Cu-Al alloy

    Science.gov (United States)

    Yoshitake, Michiko; Song, Weijie; Libra, Jiří; Mašek, Karel; Šutara, František; Matolín, Vladimír; Prince, Kevin C.

    2008-02-01

    Epitaxial ultrathin alumina films were grown on a Cu-9 at. % Al(111) substrate by selective oxidation of Al in the alloy in ultrahigh vacuum. The photoelectron spectra of Al 2p and valence band were measured in situ during oxidation. By analyzing multiple peaks of Al 2p, the interface atomic structure was discussed. The energy difference between the Fermi level of the substrate and the valence band maximum of alumina (band offset) was obtained. The relation between the interface atomic structure and the band offset was compared with the reported first-principles calculations. A novel method for controlling the band offset was proposed.

  6. Spectroscopic determination of valence band parameters in InP

    International Nuclear Information System (INIS)

    Lewis, R.A.; Lough, B.C.C.

    2003-01-01

    Full text: The general form of the Hamiltonian for an electron or hole in a semiconductor has been given by Luttinger. The valence band is characterised by three parameters - γ 1 , γ 2 , γ 3 -now commonly known as the Luttinger parameters. Despite many investigations there is still considerable uncertainty regarding the Luttinger parameters of InP. The situation has been reviewed by Hackenberg et al. These authors themselves sought to determine the Luttinger parameters by hot-electron luminescence and discovered that many Luttinger parameter triplets were consistent with their data. We employ a spectroscopic approach to estimating valence-band parameters in InP. Calculations have been made for both the unperturbed energy levels and the energy levels in a magnetic field of acceptor impurities in semiconductors characterised by different Luttinger parameters. We compare our recent experimental data for the transitions associated with the Zn acceptor impurity in InP in magnetic fields up to 30 T to determine the most appropriate set of valence-band parameters for InP

  7. Theoretical prediction of the band offsets at the ZnO/anatase TiO{sub 2} and GaN/ZnO heterojunctions using the self-consistent ab initio DFT/GGA-1/2 method

    Energy Technology Data Exchange (ETDEWEB)

    Fang, D. Q., E-mail: fangdqphy@mail.xjtu.edu.cn; Zhang, S. L. [MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, School of Science, Xi’an Jiaotong University, Xi’an 710049 (China)

    2016-01-07

    The band offsets of the ZnO/anatase TiO{sub 2} and GaN/ZnO heterojunctions are calculated using the density functional theory/generalized gradient approximation (DFT/GGA)-1/2 method, which takes into account the self-energy corrections and can give an approximate description to the quasiparticle characteristics of the electronic structure of semiconductors. We present the results of the ionization potential (IP)-based and interfacial offset-based band alignments. In the interfacial offset-based band alignment, to get the natural band offset, we use the surface calculations to estimate the change of reference level due to the interfacial strain. Based on the interface models and GGA-1/2 calculations, we find that the valence band maximum and conduction band minimum of ZnO, respectively, lie 0.64 eV and 0.57 eV above those of anatase TiO{sub 2}, while lie 0.84 eV and 1.09 eV below those of GaN, which agree well with the experimental data. However, a large discrepancy exists between the IP-based band offset and the calculated natural band offset, the mechanism of which is discussed. Our results clarify band alignment of the ZnO/anatase TiO{sub 2} heterojunction and show good agreement with the GW calculations for the GaN/ZnO heterojunction.

  8. Stability and band offsets between c-plane ZnO semiconductor and LaAlO3 gate dielectric

    Science.gov (United States)

    Wang, Jianli; Chen, Xinfeng; Wu, Shuyin; Tang, Gang; Zhang, Junting; Stampfl, C.

    2018-03-01

    Wurtzite-perovskite heterostructures composed of a high dielectric constant oxide and a wide bandgap semiconductor envision promising applications in field-effect transistors. In the present paper, the structural and electronic properties of LaAlO3/ZnO heterojunctions are investigated by first-principles calculations. We study the initial adsorption of La, Al, and oxygen atoms on ZnO (0001) and (000 1 ¯ ) surfaces and find that La atoms may occupy interstitial sites during the growth of stoichiometric ZnO (0001). The band gap of the stoichiometric ZnO (0001) surface is smaller than that of the stoichiometric ZnO (000 1 ¯ ) surface. The surface formation energy indicates that La or Al atoms may substitute Zn atoms at the nonstoichiometric ZnO (0001) surface. The atomic charges, electronic density of states, and band offsets are analyzed for the optimized LaAlO3/ZnO heterojunctions. There is a band gap for the LaAlO3/ZnO (000 1 ¯ ) heterostructures, and the largest variation in charge occurs at the surface or interface. Our results suggest that the Al-terminated LaAlO3/ZnO (000 1 ¯ ) interfaces are suitable for the design of metal oxide semiconductor devices because the valence and conduction band offsets are both larger than 1 eV and the interface does not produce any in-gap states.

  9. Valence band variation in Si (110) nanowire induced by a covered insulator

    International Nuclear Information System (INIS)

    Hong-Hua, Xu; Xiao-Yan, Liu; Yu-Hui, He; Gang, Du; Ru-Qi, Han; Jin-Feng, Kang; Chun, Fan; Ai-Dong, Sun

    2010-01-01

    In this work, we investigate strain effects induced by the deposition of gate dielectrics on the valence band structures in Si (110) nanowire via the simulation of strain distribution and the calculation of a generalized 6×6k·p strained valence band. The nanowire is surrounded by the gate dielectric. Our simulation indicates that the strain of the amorphous SiO 2 insulator is negligible without considering temperature factors. On the other hand, the thermal residual strain in a nanowire with amorphous SiO 2 insulator which has negligible lattice misfit strain pushes the valence subbands upwards by chemical vapour deposition and downwards by thermal oxidation treatment. In contrast with the strain of the amorphous SiO 2 insulator, the strain of the HfO 2 gate insulator in Si (110) nanowire pushes the valence subbands upwards remarkably. The thermal residual strain by HfO 2 insulator contributes to the up-shifting tendency. Our simulation results for valence band shifting and warping in Si nanowires can provide useful guidance for further nanowire device design. (classical areas of phenomenology)

  10. Electronic structures and valence band splittings of transition metals doped GaNs

    International Nuclear Information System (INIS)

    Lee, Seung-Cheol; Lee, Kwang-Ryeol; Lee, Kyu-Hwan

    2007-01-01

    For a practical viewpoint, presence of spin splitting of valence band in host semiconductors by the doping of transition metal (TM) ions is an essential property when designing a diluted magnetic semiconductors (DMS) material. The first principle calculations were performed on the electronic and magnetic structure of 3d transition metal doped GaN. V, Cr, and Mn doped GaNs could not be candidates for DMS materials since most of their magnetic moments is concentrated on the TM ions and the splittings of valence band were negligible. In the cases of Fe, Co, Ni, and Cu doped GaNs, on the contrary, long-ranged spin splitting of valence band was found, which could be candidates for DMS materials

  11. Location of the valence band maximum in the band structure of anisotropic 1 T'-ReSe2

    Science.gov (United States)

    Eickholt, P.; Noky, J.; Schwier, E. F.; Shimada, K.; Miyamoto, K.; Okuda, T.; Datzer, C.; Drüppel, M.; Krüger, P.; Rohlfing, M.; Donath, M.

    2018-04-01

    Transition-metal dichalcogenides (TMDCs) are a focus of current research due to their fascinating optical and electronic properties with possible technical applications. ReSe2 is an interesting material of the TMDC family, with unique anisotropic properties originating from its distorted 1 T structure (1 T '). To develop a fundamental understanding of the optical and electric properties, we studied the underlying electronic structure with angle-resolved photoemission (ARPES) as well as band-structure calculations within the density functional theory (DFT)-local density approximation (LDA) and GdW approximations. We identified the Γ ¯M¯1 direction, which is perpendicular to the a axis, as a distinct direction in k space with the smallest bandwidth of the highest valence band. Using photon-energy-dependent ARPES, two valence band maxima are identified within experimental limits of about 50 meV: one at the high-symmetry point Z , and a second one at a non-high-symmetry point in the Brillouin zone. Thus, the position in k space of the global valence band maximum is undecided experimentally. Theoretically, an indirect band gap is predicted on a DFT-LDA level, while quasiparticle corrections lead to a direct band gap at the Z point.

  12. Systematic study on intermolecular valence-band dispersion in molecular crystalline films

    International Nuclear Information System (INIS)

    Yamane, Hiroyuki; Kosugi, Nobuhiro

    2015-01-01

    Highlights: • Intermolecular valence-band dispersion of crystalline films of phthalocyanines. • Intermolecular transfer integral versus lattice constant. • Site-specific intermolecular interaction and resultant valence-band dispersion. • Band narrowing effect induced by elevated temperature. - Abstract: Functionalities of organic semiconductors are governed not only by individual properties of constituent molecules but also by solid-state electronic states near the Fermi level such as frontier molecular orbitals, depending on weak intermolecular interactions in various conformations. The individual molecular property has been widely investigated in detail; on the other hand, the weak intermolecular interaction is difficult to investigate precisely due to the presence of the structural and thermal energy broadenings in organic solids. Here we show quite small but essential intermolecular valence band dispersions and their temperature dependence of sub-0.1-eV scale in crystalline films of metal phthalocyanines (H_2Pc, ZnPc, CoPc, MnPc, and F_1_6ZnPc) by using angle-resolved photoemission spectroscopy (ARPES) with synchrotron radiation. The observed bands show intermolecular and site dependent dispersion widths, phases, and periodicities, for different chemical substitution of terminal groups and central metals in the phthalocyanine molecule. The precise and systematic band-dispersion measurement would be a credible approach toward the comprehensive understanding of intermolecular interactions and resultant charge transport properties as well as their tuning by substituents in organic molecular systems.

  13. Determination of band alignment in the single-layer MoS2/WSe2 heterojunction

    KAUST Repository

    Chiu, Ming-Hui; Zhang, Chendong; Shiu, Hung-Wei; Chuu, Chih-Piao; Chen, Chang-Hsiao; Chang, Chih-Yuan S.; Chen, Chia-Hao; Chou, Mei-Yin; Shih, Chih-Kang; Li, Lain-Jong

    2015-01-01

    The emergence of two-dimensional electronic materials has stimulated proposals of novel electronic and photonic devices based on the heterostructures of transition metal dichalcogenides. Here we report the determination of band offsets in the heterostructures of transition metal dichalcogenides by using microbeam X-ray photoelectron spectroscopy and scanning tunnelling microscopy/spectroscopy. We determine a type-II alignment between MoS2 and WSe2 with a valence band offset value of 0.83 eV and a conduction band offset of 0.76 eV. First-principles calculations show that in this heterostructure with dissimilar chalcogen atoms, the electronic structures of WSe2 and MoS2 are well retained in their respective layers due to a weak interlayer coupling. Moreover, a valence band offset of 0.94 eV is obtained from density functional theory, consistent with the experimental determination.

  14. Determination of band alignment in the single-layer MoS2/WSe2 heterojunction

    KAUST Repository

    Chiu, Ming-Hui

    2015-07-16

    The emergence of two-dimensional electronic materials has stimulated proposals of novel electronic and photonic devices based on the heterostructures of transition metal dichalcogenides. Here we report the determination of band offsets in the heterostructures of transition metal dichalcogenides by using microbeam X-ray photoelectron spectroscopy and scanning tunnelling microscopy/spectroscopy. We determine a type-II alignment between MoS2 and WSe2 with a valence band offset value of 0.83 eV and a conduction band offset of 0.76 eV. First-principles calculations show that in this heterostructure with dissimilar chalcogen atoms, the electronic structures of WSe2 and MoS2 are well retained in their respective layers due to a weak interlayer coupling. Moreover, a valence band offset of 0.94 eV is obtained from density functional theory, consistent with the experimental determination.

  15. Interface dependence of band offsets in lattice-matched isovalent heterojunctions

    Science.gov (United States)

    Lambrecht, Walter R. L.; Segall, Benjamin

    1990-01-01

    Using a previously developed self-consistent dipole theory, we find that the interface dependence of band offsets for lattice-matched isovalent heterojunction is generally small. Specifically, we find the difference between the (001) and (110) band offsets for the common-anion heterojunctions AlP/GaP, AlAs/GaAs, AlSb/GaSb, and CdTe/HgTe to be, at most, 0.02 eV. An investigation of the various details in the calculations leads to an error estimate of +/-0.03 eV; the differences are therefore insignificant. For the noncommon-anion systems, the difference between two different bonding configurations of the (001) interface is noted. Although the differences between the various interfaces are found to be slightly larger than for the common-anion cases, the only significant difference is found to occur between the In-Sb and Ga-As (001) interfaces, where it is 0.1 eV. In this case, the (110) band offset lies midway between the two.

  16. Evaluation of band alignment of α-Ga2O3/α-(Al x Ga1‑ x )2O3 heterostructures by X-ray photoelectron spectroscopy

    Science.gov (United States)

    Uchida, Takayuki; Jinno, Riena; Takemoto, Shu; Kaneko, Kentaro; Fujita, Shizuo

    2018-04-01

    The band alignment at an α-Ga2O3/α-(Al x Ga1‑ x )2O3 heterointerface, with different Al compositions (x), grown on a c-plane sapphire substrate was evaluated by X-ray photoelectron spectroscopy. The experimental results show that the heterointerface has the type-I band discontinuity with the valence band offsets of 0.090, 0.12, and 0.14 eV, and the conduction band offsets of 0.34, 0.79, and 1.87 eV, for x values of 0.1, 0.4, and 0.8, respectively. The small band offset for the valence band is attributed to the fact that the valence band of oxides is constituted by the localized O 2p level, which is dominated by the nature of oxygen atoms. The type-I band discontinuity is desirable for a variety of heterostructure devices.

  17. Nature of the valence band states in Bi2(Ca, Sr, La)3Cu2O8

    International Nuclear Information System (INIS)

    Wells, B.O.; Lindberg, P.A.P.; Shen, Z.; Dessau, D.S.; Spicer, W.E.; Lindau, I.; Mitzi, D.B.; Kapitulnik, A.

    1990-01-01

    We have used photoemission spectroscopy to examine the symmetry of the occupied states of the valence band for the La doped superconductor Bi 2 (Ca, Sr, La) 3 Cu 2 O 8 . While the oxygen states near the bottom of the 7 eV wide valence band exhibit predominantly O 2p z symmetry, the states at the top of the valence band extending to the Fermi level are found to have primarily O 2p x and O 2p y character. We have also examined anomalous intensity enhancements in the valence band feature for photon energies near 18 eV. These enhancements, which occur at photon energies ranging from 15.8 to 18.0 eV for the different valence band features, are not consistent with either simple final state effects or direct O2s transitions to unoccupied O2p states

  18. Band offset in zinc oxy-sulfide/cubic-tin sulfide interface from X-ray photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Sanal, K.C.; Nair, P.K.; Nair, M.T.S., E-mail: mtsn@ier.unam.mx

    2017-02-28

    Highlights: • Zinc oxy-sulfide thin films, 175–240 nm, deposited by rf-sputtering from targets of ZnO + ZnS. • Oxygen content in thin films is enhanced 3–4 times compared with that in ZnO:ZnS targets. • Thin film ZnO{sub x}S{sub 1−x} with x = 0.88–0.27 and optical band gap 2.8–3.2 eV is suitable for solar cells. • The conduction band offset with SnS of cubic structure studied by XPS are +0.41 to −0.28 eV. - Abstract: Zinc oxy-sulfide, ZnO{sub x}S{sub 1−x}, has been found to provide better band alignment in thin film solar cells of tin sulfide of orthorhombic crystalline structure. Here we examine ZnO{sub x}S{sub 1−x}/SnS-CUB interface, in which the ZnO{sub x}S{sub 1−x} thin film was deposited by radio frequency (rf) magnetron sputtering on SnS thin film of cubic (CUB) crystalline structure with a band gap (E{sub g}) of 1.72 eV, obtained via chemical deposition. X-ray photoelectron spectroscopy provides the valence band maxima of the materials and hence places the conduction band offset of 0.41 eV for SnS-CUB/ZnO{sub 0.27}S{sub 0.73} and −0.28 eV for SnS-CUB/ZnO{sub 0.88}S{sub 0.12} interfaces. Thin films of ZnO{sub x}S{sub 1−x} with 175–240 nm in thickness were deposited from targets prepared with different ZnO to ZnS molar ratios. With the target of molar ratio of 1:13.4, the thin films are of composition ZnO{sub 0.27}S{sub 0.73} with hexagonal crystalline structure and with that of 1:1.7 ratio, it is ZnO{sub 0.88}S{sub 0.12}. The optical band gap of the ZnO{sub x}S{sub 1−x} thin films varies from 2.90 eV to 3.21 eV as the sulfur to zinc ratio in the film increases from 0.12:1 to 0.73:1 as determined from X-ray diffraction patterns. Thus, band offsets sought for absorber materials and zinc oxy-sulfide in solar cells may be achieved through a choice of ZnO:ZnS ratio in the sputtering target.

  19. Crossover and valence band Kβ X-rays of chromium oxides

    International Nuclear Information System (INIS)

    Fazinic, Stjepko; Mandic, Luka; Kavcic, Matjaz; Bozicevic, Iva

    2011-01-01

    Kβ X-ray spectra of chromium metal and selected chromium oxides were measured twice using medium resolution flat crystal spectrometer and high resolution spectrometer employing Johansson geometry after excitation with 2 MeV proton beams. The positions and intensities of crossover (Kβ'') and valence (Kβ 2,5 ) band X-rays relative to the primary Kβ X-ray components were extracted in a consistent way. The results were compared with the existing data obtained by proton and photon induced ionization mechanisms and theoretical predictions. The obtained results in peak relative positions and intensities were analyzed in order to study dependence on the chromium oxidation states and chromium-oxygen bond lengths in selected chromium oxides. Our results obtained by both spectrometers confirm that the linear trend observed for the valence peak relative energy shift as a function of chromium oxidation number does not depend on the experimental resolution. Experimental results for normalized intensities (i.e. relative intensities divided with the number of chromium-oxygen pairs) of crossover and valence band X-rays obtained by both spectrometers are in very good agreement, and follow exponential relationship with the average Cr-O bond lengths in corresponding chromium oxides. The observed trends in crossover and valence X-rays normalized intensities could be used to measure the average chromium-oxygen bond length in various chromium oxides, with the sum of both crossover and valence X-ray normalized intensities being the most sensitive measure.

  20. Atomic contributions to the valence band photoelectron spectra of metal-free, iron and manganese phthalocyanines

    Energy Technology Data Exchange (ETDEWEB)

    Bidermane, I., E-mail: ieva.bidermane@physics.uu.se [Department of Physics and Astronomy, Uppsala University, Box-516, 75120 Uppsala (Sweden); Institut des Nanosciences de Paris, UPMC Univ. Paris 06, CNRS UMR 7588, F-75005 Paris (France); Brumboiu, I.E. [Department of Physics and Astronomy, Uppsala University, Box-516, 75120 Uppsala (Sweden); Totani, R. [Department of Physical and Chemical Sciences, University of L’Aquila, Via Vetoio, Coppito, I-67010 L’Aquila (Italy); Grazioli, C. [CNR-IOM, Laboratorio TASC, ss. 14 km. 163.5, Basovizza, 34149 Trieste (Italy); Departement of Chemical and Pharmaceutical Sciences, University of Trieste (Italy); Shariati-Nilsson, M.N.; Herper, H.C.; Eriksson, O.; Sanyal, B. [Department of Physics and Astronomy, Uppsala University, Box-516, 75120 Uppsala (Sweden); Ressel, B. [University of Nova Gorica, Vipavska Cesta 11c, 5270 Ajdovščina (Slovenia); Simone, M. de [CNR-IOM, Laboratorio TASC, ss. 14 km. 163.5, Basovizza, 34149 Trieste (Italy); Lozzi, L. [Department of Physical and Chemical Sciences, University of L’Aquila, Via Vetoio, Coppito, I-67010 L’Aquila (Italy); Brena, B.; Puglia, C. [Department of Physics and Astronomy, Uppsala University, Box-516, 75120 Uppsala (Sweden)

    2015-11-15

    Highlights: • In detail comparison between the valence band structure of H{sub 2}Pc, FePc and MnPc. • Comparison between the gas phase samples and thin evaporated films on Au (1 1 1). • Detailed analysis of the atomic orbital contributions to the valence band features. • DFT/HSE06 study of the valence band electronic structure of H{sub 2}Pc, FePc and MnPc. - Abstract: The present work reports a photoelectron spectroscopy study of the low-energy region of the valence band of metal-free phthalocyanine (H{sub 2}Pc) compared with those of iron phthalocyanine (FePc) and manganese phthalocyanine (MnPc). We have analysed in detail the atomic orbital composition of the valence band both experimentally, by making use of the variation in photoionization cross-sections with photon energy, and theoretically, by means of density functional theory. The atomic character of the Highest Occupied Molecular Orbital (HOMO), reflected on the outermost valence band binding energy region, is different for MnPc as compared to the other two molecules. The peaks related to the C 2p contributions, result in the HOMO for H{sub 2}Pc and FePc and in the HOMO-1 for MnPc as described by the theoretical predictions, in very good agreement with the experimental results. The DFT simulations, discerning the atomic contribution to the density of states, indicate how the central metal atom interacts with the C and N atoms of the molecule, giving rise to different partial and total density of states for these three Pc molecules.

  1. Valence-band splitting energies in wurtzite InP nanowires: Photoluminescence spectroscopy and ab initio calculations

    Science.gov (United States)

    Gadret, E. G.; Dias, G. O.; Dacal, L. C. O.; de Lima, M. M., Jr.; Ruffo, C. V. R. S.; Iikawa, F.; Brasil, M. J. S. P.; Chiaramonte, T.; Cotta, M. A.; Tizei, L. H. G.; Ugarte, D.; Cantarero, A.

    2010-09-01

    We investigated experimentally and theoretically the valence-band structure of wurtzite InP nanowires. The wurtzite phase, which usually is not stable for III-V phosphide compounds, has been observed in InP nanowires. We present results on the electronic properties of these nanowires using the photoluminescence excitation technique. Spectra from an ensemble of nanowires show three clear absorption edges separated by 44 meV and 143 meV, respectively. The band edges are attributed to excitonic absorptions involving three distinct valence-bands labeled: A, B, and C. Theoretical results based on “ab initio” calculation gives corresponding valence-band energy separations of 50 meV and 200 meV, respectively, which are in good agreement with the experimental results.

  2. High temperature and low pressure chemical vapor deposition of silicon nitride on AlGaN: Band offsets and passivation studies

    Energy Technology Data Exchange (ETDEWEB)

    Reddy, Pramod; Washiyama, Shun; Kaess, Felix; Hernandez-Balderrama, Luis H.; Haidet, Brian B.; Alden, Dorian; Franke, Alexander; Sarkar, Biplab; Kohn, Erhard; Collazo, Ramon; Sitar, Zlatko [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7919 (United States); Hayden Breckenridge, M. [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7919 (United States); REU, Physics Department at Wofford College, Spartanburg, South Carolina 29303 (United States)

    2016-04-14

    In this work, we employed X-ray photoelectron spectroscopy to determine the band offsets and interface Fermi level at the heterojunction formed by stoichiometric silicon nitride deposited on Al{sub x}Ga{sub 1-x}N (of varying Al composition “x”) via low pressure chemical vapor deposition. Silicon nitride is found to form a type II staggered band alignment with AlGaN for all Al compositions (0 ≤ x ≤ 1) and present an electron barrier into AlGaN even at higher Al compositions, where E{sub g}(AlGaN) > E{sub g}(Si{sub 3}N{sub 4}). Further, no band bending is observed in AlGaN for x ≤ 0.6 and a reduced band bending (by ∼1 eV in comparison to that at free surface) is observed for x > 0.6. The Fermi level in silicon nitride is found to be at 3 eV with respect to its valence band, which is likely due to silicon (≡Si{sup 0/−1}) dangling bonds. The presence of band bending for x > 0.6 is seen as a likely consequence of Fermi level alignment at Si{sub 3}N{sub 4}/AlGaN hetero-interface and not due to interface states. Photoelectron spectroscopy results are corroborated by current-voltage-temperature and capacitance-voltage measurements. A shift in the interface Fermi level (before band bending at equilibrium) from the conduction band in Si{sub 3}N{sub 4}/n-GaN to the valence band in Si{sub 3}N{sub 4}/p-GaN is observed, which strongly indicates a reduction in mid-gap interface states. Hence, stoichiometric silicon nitride is found to be a feasible passivation and dielectric insulation material for AlGaN at any composition.

  3. Interfacial chemical bonding state and band alignment of CaF2/hydrogen-terminated diamond heterojunction

    International Nuclear Information System (INIS)

    Liu, J. W.; Liao, M. Y.; Cheng, S. H.; Imura, M.; Koide, Y.

    2013-01-01

    CaF 2 films are deposited on hydrogen-terminated diamond (H-diamond) by a radio-frequency sputter-deposition technique at room temperature. Interfacial chemical bonding state and band alignment of CaF 2 /H-diamond heterojunction are investigated by X-ray photoelectron spectroscopy. It is confirmed that there are only C-Ca bonds at the CaF 2 /H-diamond heterointerface. Valence and conductance band offsets of the CaF 2 /H-diamond heterojunciton are determined to be 3.7 ± 0.2 and 0.3 ± 0.2 eV, respectively. It shows a type I straddling band configuration. The large valence band offset suggests advantage of the CaF 2 /H-diamond heterojunciton for the development of high power and high frequency field effect transistors.

  4. Valence Band Structure of InAs1-xBix and InSb1-xBix Alloy Semiconductors Calculated Using Valence Band Anticrossing Model

    Directory of Open Access Journals (Sweden)

    D. P. Samajdar

    2014-01-01

    Full Text Available The valence band anticrossing model has been used to calculate the heavy/light hole and spin-orbit split-off energies in InAs1-xBix and InSb1-xBix alloy systems. It is found that both the heavy/light hole, and spin-orbit split E+ levels move upwards in energy with an increase in Bi content in the alloy, whereas the split E− energy for the holes shows a reverse trend. The model is also used to calculate the reduction of band gap energy with an increase in Bi mole fraction. The calculated values of band gap variation agree well with the available experimental data.

  5. Relaxation and cross section effects in valence band photoemission spectroscopy

    International Nuclear Information System (INIS)

    McFeely, F.R.

    1976-09-01

    Various problems relating to the interpretation of valence band x-ray photoemission (XPS) spectra of solids are discussed. The experiments and calculations reported herein deal with the following questions: (1) To what extent do many-body effects manifest themselves in an XPS valence band spectrum, and thus invalidate a direct comparison between the photoemission energy distribution, I(E), and the density of states, N(E), calculated on the basis of ground-state one-electron theory. (2) The effect of the binding-energy-dependent photoemission cross section on I(E) at XPS energies. (3) In favorable cases indicated by (1) and (2) we examine the effect of the interaction of the crystal field with the apparent spin-orbit splittings of core levels observed in XPS spectra. (4) The use of tight binding band structure calculations to parameterize the electronic band structure from XPS and other data is described. (5) The use of high energy angle-resolved photoemission on oriented single crystals to gain orbital symmetry information is discussed. (6) The evolution of the shape of the photoemission energy distribution (of polycrystalline Cu) as a function of photon energy from 50 less than or equal h ω less than or equal 175 is discussed

  6. Band width and multiple-angle valence-state mapping of diamond

    International Nuclear Information System (INIS)

    Jimenez, I.; Terminello, L.J.; Sutherland, D.G.J.

    1997-01-01

    The band width may be considered the single most important parameter characterizing the electronic structure of a solid. The ratio of band width and Coulomb repulsion determines how correlated or delocalized an electron system is. Some of the most interesting solids straddle the boundary between localized and delocalized, e.g. the high-temperature superconductors. The bulk of the band calculations available today is based on local density functional (DF) theory. Even though the Kohn-Sham eigenvalues from that theory do not represent the outcome of a band-mapping experiment, they are remarkably similar to the bands mapped via photoemission. Strictly speaking, one should use an excited state calculation that takes the solid's many-body screening response to the hole created in photoemission into account. Diamond is a useful prototype semiconductor because of its low atomic number and large band width, which has made it a long-time favorite for testing band theory. Yet, the two experimental values of the band width of diamond have error bars of ±1 eV and differ by 3.2 eV. To obtain an accurate valence band width for diamond, the authors use a band-mapping method that collects momentum distributions instead of the usual energy distributions. This method has undergone extensive experimental and theoretical tests in determining the band width of lithium fluoride. An efficient, imaging photoelectron spectrometer is coupled with a state-of-the-art undulator beam line at the Advanced Light Source to allow collection of a large number of data sets. Since it takes only a few seconds to take a picture of the photoelectrons emitted into a 84 degrees cone, the authors can use photon energies as high as 350 eV where the cross section for photoemission from the valence band is already quite low, but the emitted photoelectrons behave free-electron-like. This make its much easier to locate the origin of the inter-band transitions in momentum space

  7. Band width and multiple-angle valence-state mapping of diamond

    Energy Technology Data Exchange (ETDEWEB)

    Jimenez, I.; Terminello, L.J.; Sutherland, D.G.J. [Lawrence Berkeley National Lab., CA (United States)] [and others

    1997-04-01

    The band width may be considered the single most important parameter characterizing the electronic structure of a solid. The ratio of band width and Coulomb repulsion determines how correlated or delocalized an electron system is. Some of the most interesting solids straddle the boundary between localized and delocalized, e.g. the high-temperature superconductors. The bulk of the band calculations available today is based on local density functional (DF) theory. Even though the Kohn-Sham eigenvalues from that theory do not represent the outcome of a band-mapping experiment, they are remarkably similar to the bands mapped via photoemission. Strictly speaking, one should use an excited state calculation that takes the solid`s many-body screening response to the hole created in photoemission into account. Diamond is a useful prototype semiconductor because of its low atomic number and large band width, which has made it a long-time favorite for testing band theory. Yet, the two experimental values of the band width of diamond have error bars of {+-}1 eV and differ by 3.2 eV. To obtain an accurate valence band width for diamond, the authors use a band-mapping method that collects momentum distributions instead of the usual energy distributions. This method has undergone extensive experimental and theoretical tests in determining the band width of lithium fluoride. An efficient, imaging photoelectron spectrometer is coupled with a state-of-the-art undulator beam line at the Advanced Light Source to allow collection of a large number of data sets. Since it takes only a few seconds to take a picture of the photoelectrons emitted into a 84{degrees} cone, the authors can use photon energies as high as 350 eV where the cross section for photoemission from the valence band is already quite low, but the emitted photoelectrons behave free-electron-like. This make its much easier to locate the origin of the inter-band transitions in momentum space.

  8. Band gap and band offset of (GaIn)(PSb) lattice matched to InP

    Science.gov (United States)

    Köhler, F.; Böhm, G.; Meyer, R.; Amann, M.-C.

    2005-07-01

    Metastable (GaxIn1-x)(PySb1-y) layers were grown on (001) InP substrates by gas source molecular beam epitaxy. Low-temperature photoluminescence spectroscopy was applied to these heterostructures and revealed spatially indirect band-to-band recombination of electrons localized in the InP with holes in the (GaxIn1-x)(PySb1-y). In addition, samples with layer thicknesses larger than 100nm showed direct PL across the band gap of (GaxIn1-x)(PySb1-y). Band-gap energies and band offset energies of (GaxIn1-x)(PySb1-y) relative to InP were derived from these PL data. A strong bowing parameter was observed.

  9. Conduction band offset at the InN/GaN heterojunction

    International Nuclear Information System (INIS)

    Wang Kejia; Lian Chuanxin; Su Ning; Jena, Debdeep; Timler, John

    2007-01-01

    The conduction-band offset between GaN and InN is experimentally determined. InN/n-type GaN isotype heterojunctions grown by molecular beam epitaxy are observed to exhibit Schottky-junction like behavior based on rectifying vertical current flow. From capacitance-voltage measurements on the heterojunction, the Schottky barrier height is found to be ∼0.94 eV. The photocurrent spectroscopy measurement by backside illumination reveals an energy barrier height of 0.95 eV across the heterojunction, consistent with the capacitance measurement. By combining electrical transport, capacitance-voltage, and photocurrent spectroscopy measurement results, the conduction band offset between InN and GaN is estimated to be ΔE C =1.68±0.1 eV

  10. VIIRS day-night band gain and offset determination and performance

    Science.gov (United States)

    Geis, J.; Florio, C.; Moyer, D.; Rausch, K.; De Luccia, F. J.

    2012-09-01

    On October 28th, 2011, the Visible-Infrared Imaging Radiometer Suite (VIIRS) was launched on-board the Suomi National Polar-orbiting Partnership (NPP) spacecraft. The instrument has 22 spectral bands: 14 reflective solar bands (RSB), 7 thermal emissive bands (TEB), and a Day Night Band (DNB). The DNB is a panchromatic, solar reflective band that provides visible through near infrared (IR) imagery of earth scenes with radiances spanning 7 orders of magnitude. In order to function over this large dynamic range, the DNB employs a focal plane array (FPA) consisting of three gain stages: the low gain stage (LGS), the medium gain stage (MGS), and the high gain stage (HGS). The final product generated from a DNB raw data record (RDR) is a radiance sensor data record (SDR). Generation of the SDR requires accurate knowledge of the dark offsets and gain coefficients for each DNB stage. These are measured on-orbit and stored in lookup tables (LUT) that are used during ground processing. This paper will discuss the details of the offset and gain measurement, data analysis methodologies, the operational LUT update process, and results to date including a first look at trending of these parameters over the early life of the instrument.

  11. Band Offset Measurements in Atomic-Layer-Deposited Al2O3/Zn0.8Al0.2O Heterojunction Studied by X-ray Photoelectron Spectroscopy.

    Science.gov (United States)

    Yan, Baojun; Liu, Shulin; Heng, Yuekun; Yang, Yuzhen; Yu, Yang; Wen, Kaile

    2017-12-01

    Pure aluminum oxide (Al 2 O 3 ) and zinc aluminum oxide (Zn x Al 1-x O) thin films were deposited by atomic layer deposition (ALD). The microstructure and optical band gaps (E g ) of the Zn x Al 1-x O (0.2 ≤ x ≤ 1) films were studied by X-ray diffractometer and Tauc method. The band offsets and alignment of atomic-layer-deposited Al 2 O 3 /Zn 0.8 Al 0.2 O heterojunction were investigated in detail using charge-corrected X-ray photoelectron spectroscopy. In this work, different methodologies were adopted to recover the actual position of the core levels in insulator materials which were easily affected by differential charging phenomena. Valence band offset (ΔE V ) and conduction band offset (ΔE C ) for the interface of the Al 2 O 3 /Zn 0.8 Al 0.2 O heterojunction have been constructed. An accurate value of ΔE V  = 0.82 ± 0.12 eV was obtained from various combinations of core levels of heterojunction with varied Al 2 O 3 thickness. Given the experimental E g of 6.8 eV for Al 2 O 3 and 5.29 eV for Zn 0.8 Al 0.2 O, a type-I heterojunction with a ΔE C of 0.69 ± 0.12 eV was found. The precise determination of the band alignment of Al 2 O 3 /Zn 0.8 Al 0.2 O heterojunction is of particular importance for gaining insight to the design of various electronic devices based on such heterointerface.

  12. Determination of valence band parameters in ZnTe

    Energy Technology Data Exchange (ETDEWEB)

    Froehlich, D.; Noethe, A.; Reimann, K. (Duesseldorf Univ. (Germany, F.R.). Physikalisches Inst. - Lehrstuhl 2)

    1984-10-01

    The fine structure of the 2P exciton in ZnTe is studied by two-photon-absorption. The energy splitting into four states, caused by the envelope-hole coupling, allows the determination of the Luttinger parameters ..gamma../sub 2/ and ..gamma../sub 3/, which describe the complex valence band. ..gamma../sub 2/ = 0.8 and ..gamma../sub 3/ = 1.7 are obtained. These values are compared to results of other experiments mainly on 1S excitons.

  13. Optical verification of the valence band structure of cadmium arsenide

    NARCIS (Netherlands)

    Gelten, M.J.; Es, van C.M.; Blom, F.A.P.; Jongeneelen, J.W.F.

    1980-01-01

    Optical absorption measurements were performed on thin single crystalline samples of Cd3As2 at temperatures of 300 K and 10 K. At low temperature the interband absorption coefficient shows clearly two steps due to direct transitions from the heavy hole and light hole valence bands to the conduction

  14. Ab initio calculation of band alignment of epitaxial La2O3 on Si(111 substrate

    Directory of Open Access Journals (Sweden)

    Alberto Debernardi

    2015-08-01

    Full Text Available By means of plane wave pseudopotential method we have studied the electronic properties of the heterostructure formed by an high dielectric constant (k oxide, the hexagonal La2O3 epitaxially grown with (0001-orientation on Si (111 substrate. We found that for La2O3 both the dielectric constant along the growth direction and the band gap are larger in the epitaxial film than in the bulk. By super-cell techniques we have computed the band alignment of the junction finding a valence band offset and a conduction band offset of ~1.6 eV and ~1.7 eV respectively. We demonstrate that the band alignment can be engineered by δ-doping the interface: our simulations show that, by doping the interface with S or Se monolayer, the valence (conduction band offset increases (decreases of about 0.5 eV without the formation of spurious electronic states in the semiconductor band-gap. The simulation of the critical thickness of pseudomorphic Lanthana film complete the work. Our results are relevant for the realization of a new generation of devices based on ultra-scaled complementary metal oxides semiconductors (CMOS technology.

  15. Accounting for many-body correlation effects in the calculation of the valence band photoelectron emission spectra of ferromagnets

    International Nuclear Information System (INIS)

    Minar, J.; Chadov, S.; Ebert, H.; Chioncel, L.; Lichtenstein, A.; De Nadai, C.; Brookes, N.B.

    2005-01-01

    The influence of dynamical correlation effects on the valence band photoelectron emission of ferromagnetic Fe, Co and Ni has been investigated. Angle-resolved as well as angle-integrated valence band photoelectron emission spectra were calculated on the basis of the one-particle Green's function, which was obtained by using the fully relativistic Korringa-Kohn-Rostoker method. The correlation effects have been included in terms of the electronic self-energy which was calculated self-consistently within Dynamical Mean-Field Theory (DMFT). In addition a theoretical approach to calculate high-energy angle-resolved valence band photoelectron emission spectra is presented

  16. Auger electron emission initiated by the creation of valence-band holes in graphene by positron annihilation.

    Science.gov (United States)

    Chirayath, V A; Callewaert, V; Fairchild, A J; Chrysler, M D; Gladen, R W; Mcdonald, A D; Imam, S K; Shastry, K; Koymen, A R; Saniz, R; Barbiellini, B; Rajeshwar, K; Partoens, B; Weiss, A H

    2017-07-13

    Auger processes involving the filling of holes in the valence band are thought to make important contributions to the low-energy photoelectron and secondary electron spectrum from many solids. However, measurements of the energy spectrum and the efficiency with which electrons are emitted in this process remain elusive due to a large unrelated background resulting from primary beam-induced secondary electrons. Here, we report the direct measurement of the energy spectra of electrons emitted from single layer graphene as a result of the decay of deep holes in the valence band. These measurements were made possible by eliminating competing backgrounds by employing low-energy positrons (holes by annihilation. Our experimental results, supported by theoretical calculations, indicate that between 80 and 100% of the deep valence-band holes in graphene are filled via an Auger transition.

  17. Band Alignment and Optical Properties of (ZrO20.66(HfO20.34 Gate Dielectrics Thin Films on p-Si (100

    Directory of Open Access Journals (Sweden)

    Dahlang Tahir

    2011-11-01

    Full Text Available (ZrO20.66(HfO20.34 dielectric films on p-Si (100 were grown by atomic layer deposition method, for which the conduction band offsets, valence band offsets and band gaps were obtained by using X-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy. The band gap, valence and conduction band offset values for (ZrO20.66(HfO20.34 dielectric thin film, grown on Si substrate were about 5.34, 2.35 and 1.87 eV respectively. This band alignment was similar to that of ZrO2. In addition, The dielectric function ε (k, ω, index of refraction n and the extinction coefficient k for the (ZrO20.66(HfO20.34 thin films were obtained from a quantitative analysis of REELS data by comparison to detailed dielectric response model calculations using the QUEELS-ε (k,ω-REELS software package. These optical properties are similar with ZrO2 dielectric thin films.

  18. Valence band structure of InAs(1-x)Bi(x) and InSb(1-x)Bi(x) alloy semiconductors calculated using valence band anticrossing model.

    Science.gov (United States)

    Samajdar, D P; Dhar, S

    2014-01-01

    The valence band anticrossing model has been used to calculate the heavy/light hole and spin-orbit split-off energies in InAs(1-x)Bi(x) and InSb(1-x)Bi(x) alloy systems. It is found that both the heavy/light hole, and spin-orbit split E + levels move upwards in energy with an increase in Bi content in the alloy, whereas the split E - energy for the holes shows a reverse trend. The model is also used to calculate the reduction of band gap energy with an increase in Bi mole fraction. The calculated values of band gap variation agree well with the available experimental data.

  19. Reformulated tight binding calculation for band discontinuity at CdTe/Hg xCd1-xTe heterointerfaces and their type I-type III transitions

    International Nuclear Information System (INIS)

    Ekpunobi, A.J.

    2005-01-01

    A recently reformulated tight binding method is used to calculate the valence band discontinuity at the CdTe/Hg x Cd 1-x Te interface in the s 2 p 2 configuration. The calculated valence band discontinuity of 0.31 eV at CdTe/HgTe interface is in good agreement with self-consistent calculation and accepted experimental value. Calculations were extended to alloy interfaces, which enabled the investigation of the band-offset problem at the transition point. Both valence band discontinuity ratio and conduction band discontinuity ratio show inflexions at the transition point

  20. Valence Band Structure of InAs1−xBix and InSb1−xBix Alloy Semiconductors Calculated Using Valence Band Anticrossing Model

    Science.gov (United States)

    Samajdar, D. P.; Dhar, S.

    2014-01-01

    The valence band anticrossing model has been used to calculate the heavy/light hole and spin-orbit split-off energies in InAs1−xBix and InSb1−xBix alloy systems. It is found that both the heavy/light hole, and spin-orbit split E + levels move upwards in energy with an increase in Bi content in the alloy, whereas the split E − energy for the holes shows a reverse trend. The model is also used to calculate the reduction of band gap energy with an increase in Bi mole fraction. The calculated values of band gap variation agree well with the available experimental data. PMID:24592181

  1. Spin-dependent electron-phonon coupling in the valence band of single-layer WS2

    DEFF Research Database (Denmark)

    Hinsche, Nicki Frank; Ngankeu, Arlette S.; Guilloy, Kevin

    2017-01-01

    The absence of inversion symmetry leads to a strong spin-orbit splitting of the upper valence band of semiconducting single-layer transition-metal dichalchogenides such as MoS2 or WS2. This permits a direct comparison of the electron-phonon coupling strength in states that only differ by their spin....... Here, the electron-phonon coupling in the valence band maximum of single-layer WS2 is studied by first-principles calculations and angle-resolved photoemission. The coupling strength is found to be drastically different for the two spin-split branches, with calculated values of λK=0.0021 and 0.......40 for the upper and lower spin-split valence band of the freestanding layer, respectively. This difference is somewhat reduced when including scattering processes involving the Au(111) substrate present in the experiment but it remains significant, in good agreement with the experimental results....

  2. Giant Cu 2p Resonances in CuO Valence-Band Photoemission

    NARCIS (Netherlands)

    Tjeng, L.H.; Chen, C.T.; Ghijsen, J.; Rudolf, P.; Sette, F.

    1991-01-01

    We report the observation of a giant resonance in the Cu 2p resonant-photoemission spectra of CuO. The study allows the unambiguous identification of the local Cu 3d8 configuration in the valence-band photoemission spectrum, providing conclusive evidence for the charge-transfer nature of the

  3. Band alignment of B0.14Al0.86N/Al0.7Ga0.3N heterojunction

    KAUST Repository

    Sun, Haiding; Park, Young Jae; Li, Kuang-Hui; Torres Castanedo, C. G.; Alowayed, Abdulmohsen; Detchprohm, Theeradetch; Dupuis, Russell D.; Li, Xiaohang

    2017-01-01

    Owing to large bandgaps of BAlN and AlGaN alloys, their heterojunctions have the potential to be used in deep ultraviolet and power electronic device applications. However, the band alignment of such junctions has not been identified. In this work, we investigated the band-offset parameters of a BAlN/AlGaN heterojunction grown by metalorganic vapor phase epitaxy. These specific compositions were chosen to ensure a sufficiently large band offset for deep ultraviolet and power electronic applications. High resolution transmission electron microscopy confirmed the high structural quality of the heterojunction with an abrupt interface and uniform element distribution. We employed high resolution X-ray photoemission spectroscopy to measure the core level binding energies of B 1s and Ga 2p with respect to the valence band maximum of BAlN and AlGaN layers, respectively. Then, we measured the energy separation between the B 1s and Ga 2p core levels at the interface of the heterojunction. The valence band offset was determined to be 0.40 ± 0.05 eV. As a consequence, we identified a staggered-gap (type-II) heterojunction with the conduction band offset of 1.10 ± 0.05 eV. The determination of the band alignment of the BAlN/AlGaN heterojunction facilitates the design of optical and electronic devices based on such junctions.

  4. Band alignment of B0.14Al0.86N/Al0.7Ga0.3N heterojunction

    KAUST Repository

    Sun, Haiding

    2017-09-21

    Owing to large bandgaps of BAlN and AlGaN alloys, their heterojunctions have the potential to be used in deep ultraviolet and power electronic device applications. However, the band alignment of such junctions has not been identified. In this work, we investigated the band-offset parameters of a BAlN/AlGaN heterojunction grown by metalorganic vapor phase epitaxy. These specific compositions were chosen to ensure a sufficiently large band offset for deep ultraviolet and power electronic applications. High resolution transmission electron microscopy confirmed the high structural quality of the heterojunction with an abrupt interface and uniform element distribution. We employed high resolution X-ray photoemission spectroscopy to measure the core level binding energies of B 1s and Ga 2p with respect to the valence band maximum of BAlN and AlGaN layers, respectively. Then, we measured the energy separation between the B 1s and Ga 2p core levels at the interface of the heterojunction. The valence band offset was determined to be 0.40 ± 0.05 eV. As a consequence, we identified a staggered-gap (type-II) heterojunction with the conduction band offset of 1.10 ± 0.05 eV. The determination of the band alignment of the BAlN/AlGaN heterojunction facilitates the design of optical and electronic devices based on such junctions.

  5. Photoemission investigation of the ZnSe/CdTe heterojunction band discontinuity

    International Nuclear Information System (INIS)

    Nelson, A.J.

    1995-01-01

    Synchrotron radiation soft x-ray photoemission spectroscopy and reflection high-energy electron diffraction were used to investigate the structural and electronic properties at the ZnSe/CdTe(100) heterojunction interface. ZnSe overlayers were sequentially grown in steps on p-type CdTe(100) single crystals at 200 degree C. In situ photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the Cd 4d, Zn 3d, and Te 4d core lines. The results were used to correlate the interfacial chemistry with the electronic structure and to directly determine the ZnSe/CdTe heterojunction valence band discontinuity and the consequent heterojunction band diagram. Results of these measurements reveal that the valence band offset is ΔE v =0.20 eV. copyright 1995 American Institute of Physics

  6. The localized effect of the Bi level on the valence band in the dilute bismuth GaBixAs1-x alloy

    Science.gov (United States)

    Zhao, Chuan-Zhen; Zhu, Min-Min; Wang, Jun; Wang, Sha-Sha; Lu, Ke-Qing

    2018-05-01

    The research on the temperature dependence of the band gap energy of the dilute bismuth GaBixAs1-x alloy has been done. It is found that its temperature insensitiveness is due to the enhanced localized character of the valence band state and the small decrease of the temperature coefficient for the conduction band minimum (CBM). The enhanced localized character of the valence band state is the main factor. In order to describe the localized effect of the Bi levels on the valence band, the localized energy is introduced into the Varshni's equation. It is found that the effect of the localized Bi level on the valence band becomes strong with increasing Bi content. In addition, it is found that the pressure dependence of the band gap energy of GaBixAs1-x does not seem to be influenced by the localized Bi levels. It is due to two factors. One is that the pressure dependence of the band gap energy is mainly determined by the D CBM of GaBixAs1-x. The D CBM of GaBixAs1-x is not influenced by the localized Bi levels. The other is that the small variation of the pressure coefficient for the D valence band maximum (VBM) state of GaBixAs1-x can be cancelled by the variation of the pressure coefficient for the D CBM state of GaBixAs1-x.

  7. Band Offsets and Interfacial Properties of HfAlO Gate Dielectric Grown on InP by Atomic Layer Deposition.

    Science.gov (United States)

    Yang, Lifeng; Wang, Tao; Zou, Ying; Lu, Hong-Liang

    2017-12-01

    X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy have been used to determine interfacial properties of HfO 2 and HfAlO gate dielectrics grown on InP by atomic layer deposition. An undesirable interfacial InP x O y layer is easily formed at the HfO 2 /InP interface, which can severely degrade the electrical performance. However, an abrupt interface can be achieved when the growth of the HfAlO dielectric on InP starts with an ultrathin Al 2 O 3 layer. The valence and conduction band offsets for HfAlO/InP heterojunctions have been determined to be 1.87 ± 0.1 and 2.83 ± 0.1 eV, respectively. These advantages make HfAlO a potential dielectric for InP MOSFETs.

  8. Reformulated tight binding calculation for band discontinuity at CdTe/Hg {sub x}Cd{sub 1-x}Te heterointerfaces and their type I-type III transitions

    Energy Technology Data Exchange (ETDEWEB)

    Ekpunobi, A.J. [Department of Physics and Industrial Physics, Nnamdi Azikiwe University, P.M.B. 5025, Awka, Anambra State (Nigeria)

    2005-02-25

    A recently reformulated tight binding method is used to calculate the valence band discontinuity at the CdTe/Hg {sub x}Cd{sub 1-x}Te interface in the s{sup 2}p{sup 2} configuration. The calculated valence band discontinuity of 0.31 eV at CdTe/HgTe interface is in good agreement with self-consistent calculation and accepted experimental value. Calculations were extended to alloy interfaces, which enabled the investigation of the band-offset problem at the transition point. Both valence band discontinuity ratio and conduction band discontinuity ratio show inflexions at the transition point.

  9. Tunneling emission of electrons from semiconductors' valence bands in high electric fields

    International Nuclear Information System (INIS)

    Kalganov, V. D.; Mileshkina, N. V.; Ostroumova, E. V.

    2006-01-01

    Tunneling emission currents of electrons from semiconductors to vacuum (needle-shaped GaAs photodetectors) and to a metal (silicon metal-insulator-semiconductor diodes with a tunneling-transparent insulator layer) are studied in high and ultrahigh electric fields. It is shown that, in semiconductors with the n-type conductivity, the major contribution to the emission current is made by the tunneling emission of electrons from the valence band of the semiconductor, rather than from the conduction band

  10. A Combined Theoretical and Experimental View on Valence and Conduction Band Densities of States of Lead Halide Perovskites

    Science.gov (United States)

    Kronik, Leeor; Endres, James; Egger, David A.; Kulbak, Michael; Kerner, Ross A.; Zhao, Lianfeng; Silver, Scott H.; Hodes, Gary; Rand, Barry P.; Cahen, David; Kahn, Antoine

    We present results for the valence and conduction band density of states (DOS), measured via ultraviolet and inverse photoemission spectroscopies for three lead halide perovskites. Specifically, the DOS of MAPbI3, MAPbBr3, and CsPbBr3, grown on different substrates, are compared. Theoretical DOS, calculated via hybrid density functional theory and including spin-orbit coupling, are compared to experimental data. The agreement between experiment and theory, obtained after correcting the latter for quantitative discrepancies, leads to the identification of valence and conduction band spectral features. In particular, this comparison allows for precise determination of the energy position of the band edges, namely ionization energies and electron affinities of these materials. We find an unusually low DOS at the valence band maximum (VBM) of these systems, which confirms and generalizes previous findings of strong band dispersion and low DOS at the VBM of MAPbI3. This calls for special attention when using electron spectroscopy to determine the frontier electronic states of lead halide perovskites.

  11. Control of Ge1-x-ySixSny layer lattice constant for energy band alignment in Ge1-xSnx/Ge1-x-ySixSny heterostructures

    Science.gov (United States)

    Fukuda, Masahiro; Watanabe, Kazuhiro; Sakashita, Mitsuo; Kurosawa, Masashi; Nakatsuka, Osamu; Zaima, Shigeaki

    2017-10-01

    The energy band alignment of Ge1-xSnx/Ge1-x-ySixSny heterostructures was investigated, and control of the valence band offset at the Ge1-xSnx/Ge1-x-ySixSny heterointerface was achieved by controlling the Si and Sn contents in the Ge1-x-ySixSny layer. The valence band offset in the Ge0.902Sn0.098/Ge0.41Si0.50Sn0.09 heterostructure was evaluated to be as high as 330 meV, and its conduction band offset was estimated to be 150 meV by considering the energy bandgap calculated from the theoretical prediction. In addition, the formation of the strain-relaxed Ge1-x-ySixSny layer was examined and the crystalline structure was characterized. The epitaxial growth of a strain-relaxed Ge0.64Si0.21Sn0.15 layer with the degree of strain relaxation of 55% was examined using a virtual Ge substrate. Moreover, enhancement of the strain relaxation was demonstrated by post-deposition annealing, where a degree of strain relaxation of 70% was achieved after annealing at 400 °C. These results indicate the possibility for enhancing the indirect-direct crossover with a strained and high-Sn-content Ge1-xSnx layer on a strain-relaxed Ge1-x-ySixSny layer, realizing preferable carrier confinement by type-I energy band alignment with high conduction and valence band offsets.

  12. Valence band electronic structure of Pd based ternary chalcogenide superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Lohani, H. [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400085 (India); Mishra, P. [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Goyal, R.; Awana, V.P.S. [National Physical Laboratory(CSIR), Dr. K. S. Krishnan Road, New Delhi 110012 (India); Sekhar, B.R., E-mail: sekhar@iopb.res.in [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400085 (India)

    2016-12-15

    Highlights: • VB Photoemission study and DFT calculations on Pd based ternary superconductors are presented. • Nb{sub 2}Pd{sub 0.95}S{sub 5} shows a temperature dependent pseudogap. • VB spectral features of ternary superconductors are correlated to their structural geometry. - Abstract: We present a comparative study of the valence band electronic structure of Pd based ternary chalcogenide superconductors Nb{sub 2}Pd{sub 0.95}S{sub 5}, Ta{sub 2}Pd{sub 0.97}S{sub 6} and Ta{sub 2}Pd{sub 0.97}Te{sub 6} using experimental photoemission spectroscopy and density functional based theoretical calculations. We observe a qualitatively similarity between valence band (VB) spectra of Nb{sub 2}Pd{sub 0.95}S{sub 5} and Ta{sub 2}Pd{sub 0.97}S{sub 6}. Further, we find a pseudogap feature in Nb{sub 2}Pd{sub 0.95}S{sub 5} at low temperature, unlike other two compounds. We have correlated the structural geometry with the differences in VB spectra of these compounds. The different atomic packing in these compounds could vary the strength of inter-orbital hybridization among various atoms which leads to difference in their electronic structure as clearly observed in our DOS calculations.

  13. Breakdown of rotational symmetry at semiconductor interfaces; a microscopic description of valence subband mixing

    International Nuclear Information System (INIS)

    Cortez, S.; Krebs, O.; Voisin, P.

    2000-01-01

    The recently discovered in-plane optical anisotropy of [001]-grown quantum wells offers a new theoretical and experimental insight into the electronic properties of semiconductor interfaces. We first discuss the coupling of X and Y valence bands due to the breakdown of rotation inversion symmetry at a semiconductor hetero-interface, with special attention to its dependence on effective parameters such as valence band offset. The intracell localization of Bloch functions is explained from simple theoretical arguments and evaluated numerically from a pseudo-potential microscopic model. The role of envelope functions is considered, and we discuss the specific case of non-common atom interfaces. Experimental results and applications to interface characterization are presented. These calculations give a microscopic justification, and establish the limits of the heuristic 'H BF ' model. (author)

  14. Optical gain and gain suppression of quantum-well lasers with valence band mixing

    International Nuclear Information System (INIS)

    Ahn, D.; Chuang, S.L.

    1990-01-01

    The effects of valence band mixing on the nonlinear gains of quantum-well lasers are studied theoretically. The authors' analysis is based on the multiband effective-mass theory and the density matrix formalism with intraband relaxation taken into account. The gain and the gain-suppression coefficient of a quantum-well laser are calculated from the complex optical susceptibility obtained by the density matrix formulation with the theoretical dipole moments obtained from the multiband effective-mass theory. The calculated gain spectrum shows that there are remarkable differences (both in peak amplitude and spectral shape) between our model with valence band mixing and the conventional parabolic band model. The shape of the gain spectrum calculated by the authors' model becomes more symmetric due to intraband relaxation together with nonparabolic energy dispersions and is closer to the experimental observations when compared with the conventional method using the parabolic band model and the multiband effective-mass calculation without intraband relaxation. Both give quite asymmetric gain spectra. Optical intensity in the GaAs active region is estimated by solving rate equations for the stationary states with nonlinear gain suppression. The authors calculate the mode gain for the resonant mode including the gain suppression, which results in spectral hole burning of the gain spectrum

  15. Analysis of in-band interference in noise-based frequency offset modulation

    NARCIS (Netherlands)

    Bilal, Ibrahim; Meijerink, Arjan; Bentum, Marinus Jan

    2014-01-01

    A noise-based frequency offset modulation (N-FOM) system is considered, employing a wideband noise carrier, transmit reference modulation and a self-correlation receiver. The performance of such a system in the presence of in-band interference is studied by modeling the interference as a Gaussian

  16. Band alignment of HfO{sub 2}/In{sub 0.18}Al{sub 0.82}N determined by angle-resolved x-ray photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Owen, Man Hon Samuel, E-mail: m.owen.sg@ieee.org, E-mail: yeo@ieee.org; Bhuiyan, Maruf Amin; Yeo, Yee-Chia, E-mail: m.owen.sg@ieee.org, E-mail: yeo@ieee.org [Department of Electrical and Computer Engineering, National University of Singapore, Singapore 119260 (Singapore); Zhang, Zheng; Pan, Ji Sheng [Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602 (Singapore); Tok, Eng Soon [Department of Physics, National University of Singapore, Singapore 117551 (Singapore)

    2014-07-21

    The band-alignment of atomic layer deposited (ALD)-HfO{sub 2}/In{sub 0.18}Al{sub 0.82}N was studied by high resolution angle-resolved X-ray photoelectron spectroscopy measurements. The band bending near the HfO{sub 2}/In{sub 0.18}Al{sub 0.82}N interface was investigated, and the potential variation across the interface was taken into account in the band alignment calculation. It is observed that the binding energies for N 1s and Al 2p in In{sub 0.18}Al{sub 0.82}N decreases and the corresponding extracted valence band offsets increases with increasing θ (i.e., closer to the HfO{sub 2}/In{sub 0.18}Al{sub 0.82}N interface), as a result of an upward energy band bending towards the HfO{sub 2}/In{sub 0.18}Al{sub 0.82}N interface. The resultant valence band offset and the conduction band offset for the ALD-HfO{sub 2}/In{sub 0.18}Al{sub 0.82}N interface calculated was found to be 0.69 eV and 1.01 eV, respectively.

  17. Theory of two-photon absorption by exciton states in cubic semiconductors with degenerate valence bands

    International Nuclear Information System (INIS)

    Nguyen Ai Viet; Nguyen Toan Thang.

    1987-06-01

    The coefficient of the absorption of two polarized photons is calculated for direct band gap semiconductors with degenerate valence bands. Wannier-Mott exciton states are included in both the intermediate and final states. Numerical calculations are performed for ZnSe and are compared with Sondergeld's experimental and theoretical results. (author). 11 refs, 2 tabs

  18. First-principle natural band alignment of GaN / dilute-As GaNAs alloy

    Directory of Open Access Journals (Sweden)

    Chee-Keong Tan

    2015-01-01

    Full Text Available Density functional theory (DFT calculations with the local density approximation (LDA functional are employed to investigate the band alignment of dilute-As GaNAs alloys with respect to the GaN alloy. Conduction and valence band positions of dilute-As GaNAs alloy with respect to the GaN alloy on an absolute energy scale are determined from the combination of bulk and surface DFT calculations. The resulting GaN / GaNAs conduction to valence band offset ratio is found as approximately 5:95. Our theoretical finding is in good agreement with experimental observation, indicating the upward movements of valence band at low-As content dilute-As GaNAs are mainly responsible for the drastic reduction of the GaN energy band gap. In addition, type-I band alignment of GaN / GaNAs is suggested as a reasonable approach for future device implementation with dilute-As GaNAs quantum well, and possible type-II quantum well active region can be formed by using InGaN / dilute-As GaNAs heterostructure.

  19. Convergence of valence bands for high thermoelectric performance for p-type InN

    International Nuclear Information System (INIS)

    Li, Hai-Zhu; Li, Ruo-Ping; Liu, Jun-Hui; Huang, Ming-Ju

    2015-01-01

    Band engineering to converge the bands to achieve high valley degeneracy is one of effective approaches for designing ideal thermoelectric materials. Convergence of many valleys in the valence band may lead to a high Seebeck coefficient, and induce promising thermoelectric performance of p-type InN. In the current work, we have systematically investigated the electronic structure and thermoelectric performance of wurtzite InN by using the density functional theory combined with semiclassical Boltzmann transport theory. Form the results, it can be found that intrinsic InN has a large Seebeck coefficient (254 μV/K) and the largest value of Z e T is 0.77. The transport properties of p-type InN are better than that of n-type one at the optimum carrier concentration, which mainly due to the large Seebeck coefficient for p-type InN, although the electrical conductivity of n-type InN is larger than that of p-type one. We found that the larger Seebeck coefficient for p-type InN may originate from the large valley degeneracy in the valence band. Moreover, the low minimum lattice thermal conductivity for InN is one key factor to become a good thermoelectric material. Therefore, p-type InN could be a potential material for further applications in the thermoelectric area.

  20. Internal-strain effect on the valence band of strained silicon and its correlation with the bond angles

    Energy Technology Data Exchange (ETDEWEB)

    Inaoka, Takeshi, E-mail: inaoka@phys.u-ryukyu.ac.jp; Yanagisawa, Susumu; Kadekawa, Yukihiro [Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213 (Japan)

    2014-02-14

    By means of the first-principles density-functional theory, we investigate the effect of relative atom displacement in the crystal unit cell, namely, internal strain on the valence-band dispersion of strained silicon, and find close correlation of this effect with variation in the specific bond angles due to internal strain. We consider the [111] ([110]) band dispersion for (111) ((110)) biaxial tensility and [111] ([110]) uniaxial compression, because remarkably small values of hole effective mass m* can be obtained in this dispersion. Under the practical condition of no normal stress, biaxial tensility (uniaxial compression) involves additional normal compression (tensility) and internal strain. With an increase in the internal-strain parameter, the energy separation between the highest and second-highest valence bands becomes strikingly larger, and the highest band with conspicuously small m* extends remarkably down to a lower energy region, until it intersects or becomes admixed with the second band. This is closely correlated with the change in the specific bond angles, and this change can reasonably explain the above enlargement of the band separation.

  1. Determination of the impact of Bi content on the valence band energy of GaAsBi using x-ray photoelectron spectroscopy

    Directory of Open Access Journals (Sweden)

    K. Collar

    2017-07-01

    Full Text Available We investigate the change of the valence band energy of GaAs1-xBix (0valence band energy per addition of 1 % Bi is determined for strained and unstrained thin films using a linear approximation applicable to the dilute regime. Spectroscopic ellipsometry (SE was used as a complementary technique to determine the change in GaAsBi bandgap resulting from Bi addition. Analysis of SE and XPS data together supports the conclusion that ∼75% of the reduction in the bandgap is in the valence band for a compressively strained, dilute GaAsBi thin film at room temperature.

  2. Reduction of the In-Band RCS of Microstrip Patch Antenna by Using Offset Feeding Technique

    Directory of Open Access Journals (Sweden)

    Weiwei Xu

    2014-01-01

    Full Text Available This paper presents a method for implementing a low in-band scattering design for microstrip patch antennas based on the analysis of structural mode scattering and radiation characteristics. The antenna structure is first designed to have the lowest structural mode scattering in a desired frequency band. The operating frequency band of the antenna is then changed to coincide with that of the lowest structural mode scattering by adjusting the feed position on the antenna (offset feeding to achieve an antenna with low in-band radar cross section (RCS. In order to reduce the level of cross polarization of the antenna caused by offset feeding, symmetry feeding structures for both single patch antennas and two-patch arrays are proposed. Examples that show the efficiency of the method are given, and the results illustrate that the in-band RCS of the proposed antennas can be reduced by as much as 17 dBsm for plane waves impinging from the normal direction compared to patch antennas fed by conventional methods.

  3. A Comparison of the Valence Band Structure of Bulk and Epitaxial GeTe-based Diluted Magnetic Semiconductors

    International Nuclear Information System (INIS)

    Pietrzyk, M.A.; Kowalski, B.J.; Orlowski, B.A.; Knoff, W.; Story, T.; Dobrowolski, W.; Slynko, V.E.; Slynko, E.I.; Johnson, R.L.

    2010-01-01

    In this work we present a comparison of the experimental results, which have been obtained by the resonant photoelectron spectroscopy for a set of selected diluted magnetic semiconductors based on GeTe, doped with manganese. The photoemission spectra are acquired for the photon energy range of 40-60 eV, corresponding to the Mn 3p → 3d resonances. The spectral features related to Mn 3d states are revealed in the emission from the valence band. The Mn 3d states contribution manifests itself in the whole valence band with a maximum at the binding energy of 3.8 eV. (authors)

  4. On the theory of phonoriton in cubic semiconductors with a degenerate valence band

    International Nuclear Information System (INIS)

    Nguyen Ai Viet; Nguyen Thi Que Huong; Le Qui Thong

    1992-10-01

    The ''phonoriton'' is an elementary excitation constructed from an exciton polariton and phonon in semiconductors under intense excitation by an electromagnetic wave near the exciton resonance (L.V. Keldysh and A.L. Ivanov, 1982). In this paper we develop a theory of phonoriton in direct band gap cubic semiconductor with a degenerate valence band using the simple model of J.L. Birman and B.S. Wang (1990). In addition to experimental proofs of the existence of phonoriton we propose an experiment to measure its flight time. (author). 33 refs

  5. Investigation of LO-leakage cancellation and DC-offset influence on flicker-noise in X-band mixers

    DEFF Research Database (Denmark)

    Michaelsen, Rasmus; Johansen, Tom; Tamborg, Kjeld

    2012-01-01

    This paper describes an investigation on the influences in 1/f noise of LO-leakage and DC-offset cancellation for X-band mixers. Conditions for LO-leakage cancellation and zero DC-offset is derived. Measurements on a double balanced diode mixer shows an improvement in noise figure from 14.3dB to ...

  6. Band alignment of atomic layer deposited SiO2 and HfSiO4 with (\\bar{2}01) β-Ga2O3

    Science.gov (United States)

    Carey, Patrick H., IV; Ren, Fan; Hays, David C.; Gila, Brent P.; Pearton, Stephen J.; Jang, Soohwan; Kuramata, Akito

    2017-07-01

    The valence band offset at both SiO2/β-Ga2O3 and HfSiO4/β-Ga2O3 heterointerfaces was measured using X-ray photoelectron spectroscopy. Both dielectrics were deposited by atomic layer deposition (ALD) onto single-crystal β-Ga2O3. The bandgaps of the materials were determined by reflection electron energy loss spectroscopy as 4.6 eV for Ga2O3, 8.7 eV for Al2O3 and 7.0 eV for HfSiO4. The valence band offset was determined to be 1.23 ± 0.20 eV (straddling gap, type I alignment) for ALD SiO2 on β-Ga2O3 and 0.02 ± 0.003 eV (also type I alignment) for HfSiO4. The respective conduction band offsets were 2.87 ± 0.70 eV for ALD SiO2 and 2.38 ± 0.50 eV for HfSiO4, respectively.

  7. 16O + 16O + valence neutrons in molecular orbitals structures of positive- and negative-parity superdeformed bands in 34S

    International Nuclear Information System (INIS)

    Taniguchi, Yasutaka

    2015-01-01

    The structures of superdeformed (SD) states in 34 S have been investigated using the antisymmetrized molecular dynamics and generator coordinate method (GCM). The GCM basis wave functions are calculated via energy variation with a constraint on the quadrupole deformation parameter β. By applying the GCM after parity and angular momentum projections, the coexistence of two positive- and one negative-parity SD bands are predicted, and low-lying states and other deformed bands are obtained. The SD bands have structures of 16 O + 16 O + two valence neutrons in molecular orbitals around the two 16 O cores in a cluster picture. The configurations of the two valence neutrons are δ 2 and π 2 for the positive-parity SD bands and π 1 δ 1 for the negative-parity SD band. (author)

  8. 16O + 16O + valence neutrons in molecular orbitals structures of positive- and negative-parity superdeformed bands in 34S

    International Nuclear Information System (INIS)

    Taniguchi, Yasutaka

    2014-01-01

    The structures of superdeformed (SD) states in 34 S are investigated using the antisymmetrized molecular dynamics and generator coordinate method (GCM). The GCM basis wave functions are calculated via energy variation with a constraint on the quadrupole deformation parameter β. By applying the GCM after parity and angular momentum projections, the coexistence of two positive- and one negative-parity SD bands are predicted, and low-lying states and other deformed bands are obtained. The SD bands have structures of 16 O + 16 O + two valence neutrons in molecular orbitals around the two 16 O cores in a cluster picture. The configurations of the two valence neutrons are δ 2 and π 2 for the positive-parity SD bands and π 1 δ 1 for the negative-parity SD band

  9. Band offsets of n-type electron-selective contacts on cuprous oxide (Cu{sub 2}O) for photovoltaics

    Energy Technology Data Exchange (ETDEWEB)

    Brandt, Riley E., E-mail: rbrandt@alum.mit.edu, E-mail: buonassisi@mit.edu; Lee, Yun Seog; Buonassisi, Tonio, E-mail: rbrandt@alum.mit.edu, E-mail: buonassisi@mit.edu [Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Young, Matthew; Dameron, Arrelaine; Teeter, Glenn [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Park, Helen Hejin; Chua, Danny; Gordon, Roy G. [Harvard University, Cambridge, Massachusetts 02139 (United States)

    2014-12-29

    The development of cuprous oxide (Cu{sub 2}O) photovoltaics (PVs) is limited by low device open-circuit voltages. A strong contributing factor to this underperformance is the conduction-band offset between Cu{sub 2}O and its n-type heterojunction partner or electron-selective contact. In the present work, a broad range of possible n-type materials is surveyed, including ZnO, ZnS, Zn(O,S), (Mg,Zn)O, TiO{sub 2}, CdS, and Ga{sub 2}O{sub 3}. Band offsets are determined through X-ray photoelectron spectroscopy and optical bandgap measurements. A majority of these materials is identified as having a negative conduction-band offset with respect to Cu{sub 2}O; the detrimental impact of this on open-circuit voltage (V{sub OC}) is evaluated through 1-D device simulation. These results suggest that doping density of the n-type material is important as well, and that a poorly optimized heterojunction can easily mask changes in bulk minority carrier lifetime. Promising heterojunction candidates identified here include Zn(O,S) with [S]/[Zn] ratios >70%, and Ga{sub 2}O{sub 3}, which both demonstrate slightly positive conduction-band offsets and high V{sub OC} potential. This experimental protocol and modeling may be generalized to evaluate the efficiency potential of candidate heterojunction partners for other PV absorbers, and the materials identified herein may be promising for other absorbers with low electron affinities.

  10. Band alignment and defects of the diamond zinc oxide heterojunction; Bandstruktur und Defekte der Diamant-Zinkoxid-Heterostruktur

    Energy Technology Data Exchange (ETDEWEB)

    Geithner, Peter

    2008-09-12

    Zinc oxide films were grown on diamond single crystals by rf sputtering of zinc oxide. The valence and conduction band offset was determined by photoelectron spectroscopy. A deep defect occurring in the zinc oxide films on diamond was characterized by cathodoluminescence spectroscopy. (orig.)

  11. CdSe/CdTe interface band gaps and band offsets calculated using spin-orbit and self-energy corrections

    Energy Technology Data Exchange (ETDEWEB)

    Ribeiro, M. [Centro de Pesquisas Avancadas Wernher von Braun, Av. Alice de Castro P.N. Mattosinho 301, CEP 13098-392 Campinas, SP (Brazil); Ferreira, L.G. [Departamento de Fisica dos Materiais e Mecanica, Instituto de Fisica, Universidade de Sao Paulo, 05315-970 Sao Paulo, SP (Brazil); Fonseca, L.R.C. [Center for Semiconductor Components, State University of Campinas, R. Pandia Calogeras 90, 13083-870 Campinas, SP (Brazil); Ramprasad, R. [Department of Chemical, Materials and Biomolecular Engineering, Institute of Materials Science, University of Connecticut, 97 North Eagleville Road, Storrs, CT 06269 (United States)

    2012-09-20

    We performed ab initio calculations of the electronic structures of bulk CdSe and CdTe, and their interface band alignments on the CdSe in-plane lattice parameters. For this, we employed the LDA-1/2 self-energy correction scheme to obtain corrected band gaps and band offsets. Our calculations include the spin-orbit effects for the bulk cases, which have shown to be of importance for the equilibrium systems and are possibly degraded in these strained semiconductors. Therefore, the SO showed reduced importance for the band alignment of this particular system. Moreover, the electronic structure calculated along the transition region across the CdSe/CdTe interface shows an interesting non-monotonic variation of the band gap in the range 0.8-1.8 eV, which may enhance the absorption of light for corresponding frequencies at the interface between these two materials in photovoltaic applications.

  12. Band Alignment at GaN/Single-Layer WSe2 Interface

    KAUST Repository

    Tangi, Malleswararao

    2017-02-21

    We study the band discontinuity at the GaN/single-layer (SL) WSe2 heterointerface. The GaN thin layer is epitaxially grown by molecular beam epitaxy on chemically vapor deposited SL-WSe2/c-sapphire. We confirm that the WSe2 was formed as an SL from structural and optical analyses using atomic force microscopy, scanning transmission electron microscopy, micro-Raman, absorbance, and microphotoluminescence spectra. The determination of band offset parameters at the GaN/SL-WSe2 heterojunction is obtained by high-resolution X-ray photoelectron spectroscopy, electron affinities, and the electronic bandgap values of SL-WSe2 and GaN. The valence band and conduction band offset values are determined to be 2.25 ± 0.15 and 0.80 ± 0.15 eV, respectively, with type II band alignment. The band alignment parameters determined here provide a route toward the integration of group III nitride semiconducting materials with transition metal dichalcogenides (TMDs) for designing and modeling of their heterojunction-based electronic and optoelectronic devices.

  13. Band Alignment at GaN/Single-Layer WSe2 Interface

    KAUST Repository

    Tangi, Malleswararao; Mishra, Pawan; Tseng, Chien-Chih; Ng, Tien Khee; Hedhili, Mohamed N.; Anjum, Dalaver H.; Alias, Mohd Sharizal; Wei, Nini; Li, Lain-Jong; Ooi, Boon S.

    2017-01-01

    We study the band discontinuity at the GaN/single-layer (SL) WSe2 heterointerface. The GaN thin layer is epitaxially grown by molecular beam epitaxy on chemically vapor deposited SL-WSe2/c-sapphire. We confirm that the WSe2 was formed as an SL from structural and optical analyses using atomic force microscopy, scanning transmission electron microscopy, micro-Raman, absorbance, and microphotoluminescence spectra. The determination of band offset parameters at the GaN/SL-WSe2 heterojunction is obtained by high-resolution X-ray photoelectron spectroscopy, electron affinities, and the electronic bandgap values of SL-WSe2 and GaN. The valence band and conduction band offset values are determined to be 2.25 ± 0.15 and 0.80 ± 0.15 eV, respectively, with type II band alignment. The band alignment parameters determined here provide a route toward the integration of group III nitride semiconducting materials with transition metal dichalcogenides (TMDs) for designing and modeling of their heterojunction-based electronic and optoelectronic devices.

  14. Instanton contributions to the valence band of the double Sine-Gordon potential

    International Nuclear Information System (INIS)

    Ricotta, R.M.; Escobar, C.O.

    1982-01-01

    The energy dispersion relation for the valence band of the double sine-Gordon potential is calculated, approximating the tunneling amplitude by a sum of contributions of multi-instantons and anti-instatons trajectories. The interesting feature of this potential is that they have to deal with two types of instantons, as there are two different potential barriers within one period of the potential. The results with the standard WKB approximation are compared. (Author) [pt

  15. BAND ALIGNMENT OF ULTRATHIN GIZO/SiO2/Si HETEROSTRUCTURE DETERMINED BY ELECTRON SPECTROSCOPY

    Directory of Open Access Journals (Sweden)

    Hee Jae Kang2

    2011-11-01

    Full Text Available Amorphous GaInZnO (GIZO thin films are grown on SiO2/Si substrate by the RF magnetron sputtering method. By thecombination of measured band gaps from reflection energy loss spectroscopy (REELS spectra and valence band fromX-ray photo-electron spectroscopy (XPS spectra, we have demonstrated the energy band alignment of GIZO thin films.The band gap values are 3.2 eV, 3.2 eV, 3.4eV and 3.6eV for the concentration ratios of Ga: In: Zn in GIZO thin filmsare 1:1:1, 2:2:1, 3:2:1 and 4:2:1, respectively. These are attributed to the larger band gap energy of Ga2O3 comparedwith In2O3 and ZnO. The valence band offsets (ΔEv decrease from 2.18 to 1.68 eV with increasing amount of Ga inGIZO thin films for GIZO1 to GIZO4, respectively. These experimental values of band gap and valence band offsetwill provide the further understanding in the fundamental properties of GIZO/SiO2/Si heterostructure, which will beuseful in the design, modeling and analysis of the performance devices applications.

  16. First determination of the valence band dispersion of CH3NH3PbI3 hybrid organic-inorganic perovskite

    Science.gov (United States)

    Lee, Min-I.; Barragán, Ana; Nair, Maya N.; Jacques, Vincent L. R.; Le Bolloc'h, David; Fertey, Pierre; Jemli, Khaoula; Lédée, Ferdinand; Trippé-Allard, Gaëlle; Deleporte, Emmanuelle; Taleb-Ibrahimi, Amina; Tejeda, Antonio

    2017-07-01

    The family of hybrid organic-inorganic halide perovskites is in the limelight because of their recently discovered high photovoltaic efficiency. These materials combine photovoltaic energy conversion efficiencies exceeding 22% and low-temperature and low-cost processing in solution; a breakthrough in the panorama of renewable energy. Solar cell operation relies on the excitation of the valence band electrons to the conduction band by solar photons. One factor strongly impacting the absorption efficiency is the band dispersion. The band dispersion has been extensively studied theoretically, but no experimental information was available. Herein, we present the first experimental determination of the valence band dispersion of methylammonium lead halide in the tetragonal phase. Our results pave the way for contrasting the electronic hopping or the electron effective masses in different theories by comparing to our experimental bands. We also show a significant broadening of the electronic states, promoting relaxed conditions for photon absorption, and demonstrate that the tetragonal structure associated to the octahedra network distortion below 50 °C induces only a minor modification of the electronic bands, with respect to the cubic phase at high temperature, thus minimizing the impact of the cubic-tetragonal transition on solar cell efficiencies.

  17. Band alignment at the Cu{sub 2}ZnSn(S{sub x}Se{sub 1-x}){sub 4}/CdS interface

    Energy Technology Data Exchange (ETDEWEB)

    Haight, Richard; Barkhouse, Aaron; Gunawan, Oki; Shin, Byungha; Copel, Matt; Hopstaken, Marinus; Mitzi, David B [IBM TJ Watson Research Center, P.O. Box 218, Yorktown Hts., New York 10598 (United States)

    2011-06-20

    Energy band alignments between CdS and Cu{sub 2}ZnSn(S{sub x}Se{sub 1-x}){sub 4} (CZTSSe) grown via solution-based and vacuum-based deposition routes were studied as a function of the [S]/[S+Se] ratio with femtosecond laser ultraviolet photoelectron spectroscopy, photoluminescence, medium energy ion scattering, and secondary ion mass spectrometry. Band bending in the underlying CZTSSe layer was measured via pump/probe photovoltage shifts of the photoelectron spectra and offsets were determined with photoemission under flat band conditions. Increasing the S content of the CZTSSe films produces a valence edge shift to higher binding energy and increases the CZTSSe band gap. In all cases, the CdS conduction band offsets were spikes.

  18. Band alignment of TiO2/FTO interface determined by X-ray photoelectron spectroscopy: Effect of annealing

    Directory of Open Access Journals (Sweden)

    Haibo Fan

    2016-01-01

    Full Text Available The energy band alignment between pulsed-laser-deposited TiO2 and FTO was firstly characterized using high-resolution X-ray photoelectron spectroscopy. A valence band offset (VBO of 0.61 eV and a conduction band offset (CBO of 0.29 eV were obtained across the TiO2/FTO heterointerface. With annealing process, the VBO and CBO across the heterointerface were found to be -0.16 eV and 1.06 eV, respectively, with the alignment transforming from type-I to type-II. The difference in the band alignment is believed to be dominated by the core level down-shift of the FTO substrate, which is a result of the oxidation of Sn. Current-voltage test has verified that the band alignment has a significant effect on the current transport of the heterojunction.

  19. Band alignment of TiO{sub 2}/FTO interface determined by X-ray photoelectron spectroscopy: Effect of annealing

    Energy Technology Data Exchange (ETDEWEB)

    Fan, Haibo, E-mail: hbfan@nwu.edu.cn, E-mail: liusz@snnu.edu.cn [Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710119 (China); School of Physics, Northwest University, Xi’an 710069 (China); Yang, Zhou; Ren, Xianpei; Gao, Fei [Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710119 (China); Yin, Mingli [Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710119 (China); School of Science, Xi’an Technological University, Xi’an, Shaanxi 710062 (China); Liu, Shengzhong, E-mail: hbfan@nwu.edu.cn, E-mail: liusz@snnu.edu.cn [Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710119 (China); Dalian Institute of Chemical Physics, Dalian National Laboratory for Clean Energy, Chinese Academy of Sciences, Dalian, 116023 (China)

    2016-01-15

    The energy band alignment between pulsed-laser-deposited TiO{sub 2} and FTO was firstly characterized using high-resolution X-ray photoelectron spectroscopy. A valence band offset (VBO) of 0.61 eV and a conduction band offset (CBO) of 0.29 eV were obtained across the TiO{sub 2}/FTO heterointerface. With annealing process, the VBO and CBO across the heterointerface were found to be -0.16 eV and 1.06 eV, respectively, with the alignment transforming from type-I to type-II. The difference in the band alignment is believed to be dominated by the core level down-shift of the FTO substrate, which is a result of the oxidation of Sn. Current-voltage test has verified that the band alignment has a significant effect on the current transport of the heterojunction.

  20. An offset-fed 20/30 GHz dual-band circularly polarized reflectarray antenna

    DEFF Research Database (Denmark)

    Smith, Thomas Gunst; Vesterdal, Niels; Gothelf, Ulrich

    2013-01-01

    A dual-frequency circularly polarized offset reflectarray antenna for Ka-band satellite communication is presented. The reflectarray is designed using the concentric dual split-loop element which enables full 360° phase adjustment simultaneously in two separate frequency bands. The elements have...... been optimized to suppress the cross-polar reflection. Thereafter, the element data is used for synthesis of the reflectarray layout and computation of the associated radiation patterns. The reflectarray is 400mm × 400mm and radiates LHCP at 19.95 GHz and RHCP at 29.75 GHz. Aperture efficiencies of 58......% and 60% are obtained at these frequencies, and the cross-polarization is more than 25 dB below peak gain....

  1. Decay of Wannier-Mott excitons interacting with acoustic phonon in semiconductors with a degenerate valence band

    International Nuclear Information System (INIS)

    Nguyen Toan Thang; Nguyen Ai Viet; Nguyen Hong Quang

    1987-06-01

    Decay probabilities of light and heavy excitons interacting with acoustic phonons in cubic semiconductors with a degenerate valence band are calculated. The numerical results for GaAs showed that the decay probability of the light exciton is much greater than that of the heavy one. (author). 10 refs, 1 fig

  2. Band alignment study of lattice-matched In{sub 0.49}Ga{sub 0.51}P and Ge using x-ray photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Owen, Man Hon Samuel, E-mail: m.owen.sg@ieee.org, E-mail: yeo@ieee.org; Zhou, Qian; Gong, Xiao; Yeo, Yee-Chia, E-mail: m.owen.sg@ieee.org, E-mail: yeo@ieee.org [Department of Electrical and Computer Engineering, National University of Singapore, Singapore 119260 (Singapore); Zhang, Zheng; Pan, Ji Sheng [Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602 (Singapore); Loke, Wan Khai; Wicaksono, Satrio; Yoon, Soon Fatt [School of Electrical and Electronic Engineering, Nanyang Technological University (NTU), Nanyang Avenue, Singapore 639798 (Singapore); Tok, Eng Soon [Department of Physics, National University of Singapore, Singapore 117551 (Singapore)

    2014-09-08

    Lattice-matched In{sub 0.49}Ga{sub 0.51}P was grown on a p-type Ge(100) substrate with a 10° off-cut towards the (111) by low temperature molecular beam epitaxy, and the band-alignment of In{sub 0.49}Ga{sub 0.51}P on Ge substrate was obtained by high resolution x-ray photoelectron spectroscopy. The valence band offset for the InGaP/Ge(100) interface was found to be 0.64 ± 0.12 eV, with a corresponding conduction band offset of 0.60 ± 0.12 eV. The InGaP/Ge interface is found to be of the type I band alignment.

  3. AlxGa1--xN/GaN band offsets determined by deep-level emission

    International Nuclear Information System (INIS)

    Hang, D. R.; Chen, C. H.; Chen, Y. F.; Jiang, H. X.; Lin, J. Y.

    2001-01-01

    We present studies of the compositional dependence of the optical properties of Al x Ga 1-x N(0 x Ga 1-x N. As aluminum concentration increases, the color of the band changes from yellow (2.2 eV) to blue (2.6 eV). The shift was less than that of the band gap. Together with previously published studies, it implies that the deep acceptor level is pinned to a common reference level to both materials, thus the deep level responsible for the yellow emission is used as a common reference level to determine the band alignment in Al x Ga 1-x N/GaN heterojunctions. Combining with the near-band-edge modulation spectra, the estimated ratio of conduction-to-valence band discontinuity is 65:35. Our results are close to the values obtained from PL measurements on Al 0.14 Ga 0.86 N/GaN quantum wells and those calculated by linear muffin-tin orbital method and linearized augmented plane wave method. copyright 2001 American Institute of Physics

  4. Interplay of Coulomb interactions and disorder in three-dimensional quadratic band crossings without time-reversal symmetry and with unequal masses for conduction and valence bands

    Science.gov (United States)

    Mandal, Ipsita; Nandkishore, Rahul M.

    2018-03-01

    Coulomb interactions famously drive three-dimensional quadratic band crossing semimetals into a non-Fermi liquid phase of matter. In a previous work [Nandkishore and Parameswaran, Phys. Rev. B 95, 205106 (2017), 10.1103/PhysRevB.95.205106], the effect of disorder on this non-Fermi liquid phase was investigated, assuming that the band structure was isotropic, assuming that the conduction and valence bands had the same band mass, and assuming that the disorder preserved exact time-reversal symmetry and statistical isotropy. It was shown that the non-Fermi liquid fixed point is unstable to disorder and that a runaway flow to strong disorder occurs. In this paper, we extend that analysis by relaxing the assumption of time-reversal symmetry and allowing the electron and hole masses to differ (but continuing to assume isotropy of the low energy band structure). We first incorporate time-reversal symmetry breaking disorder and demonstrate that there do not appear any new fixed points. Moreover, while the system continues to flow to strong disorder, time-reversal-symmetry-breaking disorder grows asymptotically more slowly than time-reversal-symmetry-preserving disorder, which we therefore expect should dominate the strong-coupling phase. We then allow for unequal electron and hole masses. We show that whereas asymmetry in the two masses is irrelevant in the clean system, it is relevant in the presence of disorder, such that the `effective masses' of the conduction and valence bands should become sharply distinct in the low-energy limit. We calculate the RG flow equations for the disordered interacting system with unequal band masses and demonstrate that the problem exhibits a runaway flow to strong disorder. Along the runaway flow, time-reversal-symmetry-preserving disorder grows asymptotically more rapidly than both time-reversal-symmetry-breaking disorder and the Coulomb interaction.

  5. Boron Doped diamond films as electron donors in photovoltaics: An X-ray absorption and hard X-ray photoemission study

    Energy Technology Data Exchange (ETDEWEB)

    Kapilashrami, M.; Zegkinoglou, I. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Physics, University of Wisconsin Madison, Madison, Wisconsin 53706 (United States); Conti, G.; Nemšák, S.; Conlon, C. S.; Fadley, C. S. [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Törndahl, T.; Fjällström, V. [Ångström Solar Center, Uppsala University, Box 534, SE-751 21 Uppsala (Sweden); Lischner, J. [Department of Physics, University of California, Berkeley, California 94720 (United States); Louie, Steven G. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Physics, University of California, Berkeley, California 94720 (United States); Hamers, R. J.; Zhang, L. [Department of Chemistry, University of Wisconsin Madison, Madison, Wisconsin 53706 (United States); Guo, J.-H. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Himpsel, F. J., E-mail: fhimpsel@wisc.edu [Department of Physics, University of Wisconsin Madison, Madison, Wisconsin 53706 (United States)

    2014-10-14

    Highly boron-doped diamond films are investigated for their potential as transparent electron donors in solar cells. Specifically, the valence band offset between a diamond film (as electron donor) and Cu(In,Ga)Se₂ (CIGS) as light absorber is determined by a combination of soft X-ray absorption spectroscopy and hard X-ray photoelectron spectroscopy, which is more depth-penetrating than standard soft X-ray photoelectron spectroscopy. In addition, a theoretical analysis of the valence band is performed, based on GW quasiparticle band calculations. The valence band offset is found to be small: VBO=VBM{sub CIGS} – VBM{sub diamond}=0.3 eV±0.1 eV at the CIGS/Diamond interface and 0.0 eV±0.1 eV from CIGS to bulk diamond. These results provide a promising starting point for optimizing the band offset by choosing absorber materials with a slightly lower valence band maximum.

  6. Band alignment of atomic layer deposited MgO/Zn{sub 0.8}Al{sub 0.2}O heterointerface determined by charge corrected X-ray photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Baojun, E-mail: yanbj@ihep.ac.cn [State Key Laboratory of Particle Detection and Electronics, Institute of High Energy Physics of Chinese Academy of Sciences, Beijing P. O. Box 100049 (China); Liu, Shulin [State Key Laboratory of Particle Detection and Electronics, Institute of High Energy Physics of Chinese Academy of Sciences, Beijing P. O. Box 100049 (China); Yang, Yuzhen [State Key Laboratory of Particle Detection and Electronics, Institute of High Energy Physics of Chinese Academy of Sciences, Beijing P. O. Box 100049 (China); Department of Physics, Nanjing University, Nanjing P. O. Box 210093 (China); Heng, Yuekun [State Key Laboratory of Particle Detection and Electronics, Institute of High Energy Physics of Chinese Academy of Sciences, Beijing P. O. Box 100049 (China)

    2016-05-15

    Highlights: • Band alignment of MgO/Zn{sub 0.8}Al{sub 0.2}O heterojunction were investigated systematically using charge corrected X-ray photoelectron spectroscopy. • Differential charging phenomenon is observed in determination VBOs of insulator/semiconductor heterojunction. • Valence and conduction band offsets have been determined to be 0.72 ± 0.11 eV and 3.26 ± 0.11 eV, respectively, with a type-II band line-up. - Abstract: Pure magnesium (MgO) and zinc oxide doped with aluminum oxide (Zn{sub 0.8}Al{sub 0.2}O) were prepared via atomic layer deposition. We have studied the structure and band gap of bulk Zn{sub 0.8}Al{sub 0.2}O material by X-ray diffractometer (XRD) and Tauc method, and the band offsets and alignment of atomic layer deposited MgO/Zn{sub 0.8}Al{sub 0.2}O heterointerface were investigated systematically using X-ray photoelectron spectroscopy (XPS) in this study. Different methodologies, such as neutralizing electron gun, the use of C 1s peak recalibration and zero charging method, were applied to recover the actual position of the core levels in insulator materials which were easily influenced by differential charging phenomena. Schematic band alignment diagram, valence band offset (ΔE{sub V}) and conduction band offset (ΔE{sub C}) for the interface of the MgO/Zn{sub 0.8}Al{sub 0.2}O heterostructure have been constructed. An accurate value of ΔE{sub V} = 0.72 ± 0.11 eV was obtained from various combinations of core levels of heterojunction with varied MgO thickness. Given the experimental band gaps of 7.83 eV for MgO and 5.29 eV for Zn{sub 0.8}Al{sub 0.2}O, a type-II heterojunction with a ΔE{sub C} of 3.26 ± 0.11 eV was found. Band offsets and alignment studies of these heterojunctions are important for gaining deep consideration to the design of various optoelectronic devices based on such heterointerface.

  7. Ballistic-electron-emission spectroscopy of AlxGa1-xAs/GaAs heterostructures: Conduction-band offsets, transport mechanisms, and band-structure effects

    International Nuclear Information System (INIS)

    OShea, J.J.; Brazel, E.G.; Rubin, M.E.; Bhargava, S.; Chin, M.A.; Narayanamurti, V.

    1997-01-01

    We report an extensive investigation of semiconductor band-structure effects in single-barrier Al x Ga 1-x As/GaAs heterostructures using ballistic-electron-emission spectroscopy (BEES). The transport mechanisms in these single-barrier structures were studied systematically as a function of temperature and Al composition over the full compositional range (0≤x≤1). The initial (Γ) BEES thresholds for Al x Ga 1-x As single barriers with 0≤x≤0.42 were extracted using a model which includes the complete transmission probability of the metal-semiconductor interface and the semiconductor heterostructure. Band offsets measured by BEES are in good agreement with previous measurements by other techniques which demonstrates the accuracy of this technique. BEES measurements at 77 K give the same band-offset values as at room temperature. When a reverse bias is applied to the heterostructures, the BEES thresholds shift to lower voltages in good agreement with the expected bias-induced band-bending. In the indirect band-gap regime (x>0.45), spectra show a weak ballistic-electron-emission microscopy current contribution due to intervalley scattering through Al x Ga 1-x As X valley states. Low-temperature spectra show a marked reduction in this intervalley current component, indicating that intervalley phonon scattering at the GaAs/Al x Ga 1-x As interface produces a significant fraction of thisX valley current. A comparison of the BEES thresholds with the expected composition dependence of the Al x Ga 1-x As Γ, L, and X points yields good agreement over the entire composition range. copyright 1997 The American Physical Society

  8. Twice the negativity bias and half the positivity offset: Evaluative responses to emotional information in depression.

    Science.gov (United States)

    Gollan, Jackie K; Hoxha, Denada; Hunnicutt-Ferguson, Kallio; Norris, Catherine J; Rosebrock, Laina; Sankin, Lindsey; Cacioppo, John

    2016-09-01

    Humans have the dual capacity to assign a slightly pleasant valence to neutral stimuli (the positivity offset) to encourage approach behaviors, as well as to assign a higher negative valence to unpleasant images relative to the positive valence to equally arousing and extreme pleasant images (the negativity bias) to facilitate defensive strategies. We conducted an experimental psychopathology study to examine the extent to which the negativity bias and the positivity offset differ in participants with and without major depression.. Forty-one depressed and thirty-six healthy participants were evaluated using a structured clinical interview for DSM-IV Axis I disorders, questionnaires, and a computerized task designed to measure implicit affective responses to unpleasant, neutral, and pleasant stimuli. The negativity bias was significantly higher and the positivity offset was significantly lower in depressed relative to healthy participants.. Entry criteria enrolling medication-free participants with minimal DSM-IV comorbidity may limit generalizability of the findings. This study advances our understanding of the positive and negative valence systems in depression, highlighting the irregularities in the positive valence system.. Copyright © 2015 Elsevier Ltd. All rights reserved.

  9. Valence-band and core-level photoemission study of single-crystal Bi2CaSr2Cu2O8 superconductors

    International Nuclear Information System (INIS)

    Shen, Z.; Lindberg, P.A.P.; Wells, B.O.; Mitzi, D.B.; Lindau, I.; Spicer, W.E.; Kapitulnik, A.

    1988-01-01

    High-quality single crystals of Bi 2 CaSr 2 Cu 2 O 8 superconductors have been prepared and cleaved in ultrahigh vacuum. Low-energy electron diffraction measurements show that the surface structure is consistent with the bulk crystal structure. Ultraviolet photoemission and x-ray photoemission experiments were performed on these well-characterized sample surfaces. The valence-band and the core-level spectra obtained from the single-crystal surfaces are in agreement with spectra recorded from polycrystalline samples, justifying earlier results from polycrystalline samples. Cu satellites are observed both in the valence band and Cu 2p core level, signaling the strong correlation among the Cu 3d electrons. The O 1s core-level data exhibit a sharp, single peak at 529-eV binding energy without any clear satellite structures

  10. Boron Doped diamond films as electron donors in photovoltaics: An X-ray absorption and hard X-ray photoemission study

    International Nuclear Information System (INIS)

    Kapilashrami, M.; Zegkinoglou, I.; Conti, G.; Nemšák, S.; Conlon, C. S.; Fadley, C. S.; Törndahl, T.; Fjällström, V.; Lischner, J.; Louie, Steven G.; Hamers, R. J.; Zhang, L.; Guo, J.-H.; Himpsel, F. J.

    2014-01-01

    Highly boron-doped diamond films are investigated for their potential as transparent electron donors in solar cells. Specifically, the valence band offset between a diamond film (as electron donor) and Cu(In,Ga)Se 2 (CIGS) as light absorber is determined by a combination of soft X-ray absorption spectroscopy and hard X-ray photoelectron spectroscopy, which is more depth-penetrating than standard soft X-ray photoelectron spectroscopy. In addition, a theoretical analysis of the valence band is performed, based on GW quasiparticle band calculations. The valence band offset is found to be small: VBO = VBM CIGS – VBM diamond  = 0.3 eV ± 0.1 eV at the CIGS/Diamond interface and 0.0 eV ± 0.1 eV from CIGS to bulk diamond. These results provide a promising starting point for optimizing the band offset by choosing absorber materials with a slightly lower valence band maximum.

  11. Valence-band discontinuities of wurtzite GaN, AlN, and InN heterojunctions measured by x-ray photoemission spectroscopy

    International Nuclear Information System (INIS)

    Martin, G.; Botchkarev, A.; Rockett, A.; Morkoc, H.

    1996-01-01

    The valence-band discontinuities at various wurtzite GaN, AlN, and InN heterojunctions were measured by means of x-ray photoemission spectroscopy. A significant forward endash backward asymmetry was observed in the InN/GaN endash GaN/InN and InN/AlN endash AlN/InN heterojunctions. The asymmetry was understood as a piezoelectric strain effect. We report the valence band discontinuities for InN/GaN=1.05±0.25 eV, GaN/AlN=0.70±0.24 eV, and InN/AlN=1.81±0.20 eV, all in the standard type I lineup. These values obey transitivity to within the experimental accuracy. Tables of photoemission core level binding energies are reported for wurtzite GaN, AlN, and InN. copyright 1996 American Institute of Physics

  12. Band alignments and improved leakage properties of (La2O3)0.5(SiO2)0.5/SiO2/GaN stacks for high-temperature metal-oxide-semiconductor field-effect transistor applications

    Science.gov (United States)

    Gao, L. G.; Xu, B.; Guo, H. X.; Xia, Y. D.; Yin, J.; Liu, Z. G.

    2009-06-01

    The band alignments of (La2O3)0.5(SiO2)0.5(LSO)/GaN and LSO/SiO2/GaN gate dielectric stacks were investigated comparatively by using x-ray photoelectron spectroscopy. The valence band offsets for LSO/GaN stack and LSO/SiO2/GaN stack are 0.88 and 1.69 eV, respectively, while the corresponding conduction band offsets are found to be 1.40 and 1.83 eV, respectively. Measurements of the leakage current density as function of temperature revealed that the LSO/SiO2/GaN stack has much lower leakage current density than that of the LSO/GaN stack, especially at high temperature. It is concluded that the presence of a SiO2 buffer layer increases band offsets and reduces the leakage current density effectively.

  13. Cd-free buffer layer materials on Cu2ZnSn(SxSe1-x)4: Band alignments with ZnO, ZnS, and In2S3

    Science.gov (United States)

    Barkhouse, D. Aaron R.; Haight, Richard; Sakai, Noriyuki; Hiroi, Homare; Sugimoto, Hiroki; Mitzi, David B.

    2012-05-01

    The heterojunctions formed between Cu2ZnSn(SxSe1-x)4 (CZTSSe) and three Cd-free n-type buffers, ZnS, ZnO, and In2S3, were studied using femtosecond ultraviolet photoemission and photovoltage spectroscopy. The electronic properties including the Fermi level location at the interface, band bending in the CZTSSe substrate, and valence and conduction band offsets were determined and correlated with device properties. We also describe a method for determining the band bending in the buffer layer and demonstrate this for the In2S3/CZTSSe system. The chemical bath deposited In2S3 buffer is found to have near optimal conduction band offset (0.15 eV), enabling the demonstration of Cd-free In2S3/CZTSSe solar cells with 7.6% power conversion efficiency.

  14. Features of carrier tunneling between the silicon valence band and metal in devices based on the Al/high-K oxide/SiO_2/Si structure

    International Nuclear Information System (INIS)

    Vexler, M. I.; Grekhov, I. V.

    2016-01-01

    The features of electron tunneling from or into the silicon valence band in a metal–insulator–semiconductor system with the HfO_2(ZrO_2)/SiO_2 double-layer insulator are theoretically analyzed for different modes. It is demonstrated that the valence-band current plays a less important role in structures with HfO_2(ZrO_2)/SiO_2 than in structures containing only silicon dioxide. In the case of a very wide-gap high-K oxide ZrO_2, nonmonotonic behavior related to tunneling through the upper barrier is predicted for the valence-band–metal current component. The use of an insulator stack can offer certain advantages for some devices, including diodes, bipolar tunnel-emitter transistors, and resonant-tunneling diodes, along with the traditional use of high-K insulators in a field-effect transistor.

  15. Evidence of Type-II Band Alignment in III-nitride Semiconductors: Experimental and theoretical investigation for In0.17Al0.83N/GaN heterostructures

    Science.gov (United States)

    Wang, Jiaming; Xu, Fujun; Zhang, Xia; An, Wei; Li, Xin-Zheng; Song, Jie; Ge, Weikun; Tian, Guangshan; Lu, Jing; Wang, Xinqiang; Tang, Ning; Yang, Zhijian; Li, Wei; Wang, Weiying; Jin, Peng; Chen, Yonghai; Shen, Bo

    2014-01-01

    Type-II band alignment structure is coveted in the design of photovoltaic devices and detectors, since it is beneficial for the transport of photogenerated carriers. Regrettably, for group-III-nitride wide bandgap semiconductors, all existing devices are limited to type-I heterostructures, owing to the unavailable of type-II ones. This seriously restricts the designing flexibility for optoelectronic devices and consequently the relevant performance of this material system. Here we show a brandnew type-II band alignment of the lattice-matched In0.17Al0.83N/GaN heterostructure from the perspective of both experimental observations and first-principle theoretical calculations. The band discontinuity is dominated by the conduction band offset ΔEC, with a small contribution from the valence band offset ΔEV which equals 0.1 eV (with being above). Our work may open up new prospects to realize high-performance III-Nitrides optoelectronic devices based on type-II energy band engineering. PMID:25283334

  16. Experimental determination of conduction and valence bands of semiconductor nanoparticles using Kelvin probe force microscopy

    International Nuclear Information System (INIS)

    Zhang Wen; Chen Yongsheng

    2013-01-01

    The ability to determine a semiconductor’s band edge positions is important for the design of new photocatalyst materials. In this paper, we introduced an experimental method based on Kelvin probe force microscopy to determine the conduction and valence band edge energies of semiconductor nanomaterials, which has rarely been demonstrated. We tested the method on six semiconductor nanoparticles (α-Fe 2 O 3 , CeO 2 , Al 2 O 3 , CuO, TiO 2 , and ZnO) with known electronic structures. The experimentally determined band edge positions for α-Fe 2 O 3 , Al 2 O 3 , and CuO well matched the literature values with no statistical difference. Except CeO 2 , all other metal oxides had a consistent upward bias in the experimental measurements of band edge positions because of the shielding effect of the adsorbed surface water layer. This experimental approach may outstand as a unique alternative way of probing the band edge energy positions of semiconductor materials to complement the current computational methods, which often find limitations in new synthetic or complex materials. Ultimately, this work provides scientific foundation for developing experimental tools to probe nanoscale electronic properties of photocatalytic materials, which will drive breakthroughs in the design of novel photocatalytic systems and advance the fundamental understanding of material properties.

  17. Feeling worse to feel better: pain-offset relief simultaneously stimulates positive affect and reduces negative affect.

    Science.gov (United States)

    Franklin, Joseph C; Lee, Kent M; Hanna, Eleanor K; Prinstein, Mitchell J

    2013-04-01

    Although pain itself induces negative affect, the removal (or offset) of pain induces a powerful state of relief. Despite being implicated in a wide range of psychological and behavioral phenomena, relief remains a poorly understood emotion. In particular, some theorists associate relief with increased positive affect, whereas others associate relief with diminished negative affect. In the present study, we examined the affective nature of relief in a pain-offset paradigm with psychophysiological measures that were specific to negative valence (startle eyeblink reactivity) and positive valence (startle postauricular reactivity). Results revealed that pain offset simultaneously stimulates positive affect and diminishes negative affect for at least several seconds. Results also indicated that pain intensity differentially affects the positive and negative valence aspects of relief. These findings clarify the affective nature of relief and provide insight into why people engage in both normal and abnormal behaviors associated with relief.

  18. Characterization of the Valence and Conduction Band Levels of n = 1 2D Perovskites: A Combined Experimental and Theoretical Investigation

    KAUST Repository

    Silver, Scott

    2018-02-13

    This study presents a combined experimental and theoretical study of the electronic structure of two 2D metal halide perovskite films. Ultraviolet and inverse photoemission spectroscopies are performed on solution-processed thin films of the n = 1 layered perovskite butylammonium lead iodide and bromide, BA2PbI4 and BA2PbBr4, characterized by optical absorption and X-ray diffraction, to determine their valence and conduction band densities of states, transport gaps, and exciton binding energies. The electron spectroscopy results are compared with the densities of states determined by density functional theory calculations. The remarkable agreement between experiment and calculation enables a detailed identification and analysis of the organic and inorganic contributions to the valence and conduction bands of these two hybrid perovskites. The electron affinity and ionization energies are found to be 3.1 and 5.8 eV for BA2PbI4, and 3.1 and 6.5 eV for BA2PbBr4. The exciton binding energies are estimated to be 260 and 300 meV for the two materials, respectively. The 2D lead iodide and bromide perovskites exhibit significantly less band dispersion and a larger density of states at the band edges than the 3D analogs. The effects of using various organic ligands are also discussed.

  19. Promoting SnTe as an Eco-Friendly Solution for p-PbTe Thermoelectric via Band Convergence and Interstitial Defects.

    Science.gov (United States)

    Li, Wen; Zheng, Linglang; Ge, Binghui; Lin, Siqi; Zhang, Xinyue; Chen, Zhiwei; Chang, Yunjie; Pei, Yanzhong

    2017-05-01

    Compared to commercially available p-type PbTe thermoelectrics, SnTe has a much bigger band offset between its two valence bands and a much higher lattice thermal conductivity, both of which limit its peak thermoelectric figure of merit, zT of only 0.4. Converging its valence bands or introducing resonant states is found to enhance the electronic properties, while nanostructuring or more recently introducing interstitial defects is found to reduce the lattice thermal conductivity. Even with an integration of some of the strategies above, existing efforts do not enable a peak zT exceeding 1.4 and usually involve Cd or Hg. In this work, a combination of band convergence and interstitial defects, each of which enables a ≈150% increase in the peak zT, successfully accumulates the zT enhancements to be ≈300% (zT up to 1.6) without involving any toxic elements. This opens new possibilities for further improvements and promotes SnTe as an environment-friendly solution for conventional p-PbTe thermoelectrics. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Effect of temperature on the valency bands of HDO in water in the liquid and solid states. Effects on the analysis of heavy water using infra-red absorption; Effet de temperature sur les bandes de valence de HDO dans l'eau a l'etat liquide et a l'etat solide - consequences pour l'analyse de l'eau lourde par absorption infra-rouge

    Energy Technology Data Exchange (ETDEWEB)

    Ceccaldi, M [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1964-07-01

    After, a description of the technique used, a qualitative examination is made of the influence of the temperature on the {nu}{sub OH}(3,400 cm{sup -1}) and {nu}{sub OD} (2,500 cm{sup -1}) valence bands of HDO in the liquid state and then during the passage to the solid state. Quantitative examination with two cells of different thickness makes it possible to define the influence of temperature on the residual absorption of the pure liquid (D{sub 2}O or H{sub 2}O and on the valency bands ({nu}{sub OH} and {nu}{sub OD} respectively). It is found that a similar change occurs in the two bands but that the changes in the background are very different. During the passage from the liquid to the solid state the shape of the bands varies considerably but little change occurs in the total intensity. It has been possible to express these results in a simple form which is directly applicable to analytical problems. (authors) [French] Apres un rappel de la technique utilisee, on examine qualitativement l'influence de la temperature sur les bandes de valence {nu}{sub OH} (3400 cm{sup -1}) et {nu}{sub OD} (2500 cm{sup -1}) de HDO a l'etat liquide puis le passage a l'etat solide. L'examen quantitatif, avec deux cuves d'epaisseurs differentes, permet de preciser l'influence de la temperature sur l'absorption residuelle du liquide pur (D{sub 2}O ou H{sub 2}O) et sur les bandes de valence ( {nu}{sub OH} et {nu}{sub OD} respectivement). On constate une evolution parallele de ces bandes mais un comportement tres different du fond continu. Lors du passage de l'etat liquide a l'etat solide, la forme des bandes varie considerablement mais non l'intensite totale. On a pu formuler ces resultats sous une forme simple applicable directement aux problemes analytiques. (auteurs)

  1. Valence band structure of PDMS surface and a blend with MWCNTs: A UPS and MIES study of an insulating polymer

    Energy Technology Data Exchange (ETDEWEB)

    Schmerl, Natalya M.; Khodakov, Dmitriy A.; Stapleton, Andrew J.; Ellis, Amanda V.; Andersson, Gunther G., E-mail: gunther.andersson@flinders.edu.au

    2015-10-30

    Graphical abstract: - Highlights: • Valence electron spectroscopy was performed on an insulating polymer using different charge compensation methods. • MWCNT were embedded in PDMS and found to be the most effective method for reducing the charging of the insulating polymer. • The valence band spectrum of PDMS was obtained via MIES and UPS. • Ion scattering spectroscopy was used to determine the concentration depth profile of the PDMS in the sample. - Abstract: The use of polydimethylsiloxane (PDMS) is increasing with new technologies working toward compact, flexible and transparent devices for use in medical and microfluidic systems. Electronic characterization of PDMS and other insulating materials is difficult due to charging, yet necessary for many applications where the interfacial structure is vital to device function or further modification. The outermost layer in particular is of importance as this is the area where chemical reactions such as surface functionalization will occur. Here, we investigate the valence band structure of the outermost layer and near surface area of PDMS through the use of metastable induced photoelectron spectroscopy (MIES) paired with ultraviolet photoelectron spectroscopy (UPS). The chemical composition of the samples under investigation were measured via X-ray photoelectron spectroscopy (XPS), and the vertical distribution of the polymer was shown with neutral impact collision ion scattering spectroscopy (NICISS). Three separate methods for charge compensation are used for the samples, and their effectiveness is compared.

  2. A W-Band Radiometer with the Offset Parabolic Antenna for Radiometric Measurements

    Directory of Open Access Journals (Sweden)

    Li Wu

    2016-01-01

    Full Text Available This paper deals with the development of a W-band noise-adding radiometer which combines the millimeter-wave (MMW radiometric measurements with a high-resolution imager. The offset parabolic antenna is presented to achieve an accurate measurement and a high resolution. To reduce the cross-polarization level of the antenna, a multimode feed horn with a multistep structure is proposed to match the focal region fields of the reflector. It has advantages over the corrugated horns in lower mass and easier manufacturing. In addition, due to an unavoidable settling time for the noise-adding radiometer output signal passing through the low-pass filter, a theoretical criterion for the optimum duty cycle determination to reject extraneous contributions from the transient is proposed in this paper. The appropriate duty cycle threshold is 0.33 for the developed W-band radiometer. Also, a geometric correction method is presented to correct the obtained passive image suffering from a distortion for a better image interpretation. Preliminary experimental results are given to illustrate and verify the presented techniques.

  3. Electron Band Alignment at Interfaces of Semiconductors with Insulating Oxides: An Internal Photoemission Study

    Directory of Open Access Journals (Sweden)

    Valeri V. Afanas'ev

    2014-01-01

    Full Text Available Evolution of the electron energy band alignment at interfaces between different semiconductors and wide-gap oxide insulators is examined using the internal photoemission spectroscopy, which is based on observations of optically-induced electron (or hole transitions across the semiconductor/insulator barrier. Interfaces of various semiconductors ranging from the conventional silicon to the high-mobility Ge-based (Ge, Si1-xGex, Ge1-xSnx and AIIIBV group (GaAs, InxGa1-xAs, InAs, GaP, InP, GaSb, InSb materials were studied revealing several general trends in the evolution of band offsets. It is found that in the oxides of metals with cation radii larger than ≈0.7 Å, the oxide valence band top remains nearly at the same energy (±0.2 eV irrespective of the cation sort. Using this result, it becomes possible to predict the interface band alignment between oxides and semiconductors as well as between dissimilar insulating oxides on the basis of the oxide bandgap width which are also affected by crystallization. By contrast, oxides of light elements, for example, Be, Mg, Al, Si, and Sc exhibit significant shifts of the valence band top. General trends in band lineup variations caused by a change in the composition of semiconductor photoemission material are also revealed.

  4. Electronic properties and bonding in Zr Hx thin films investigated by valence-band x-ray photoelectron spectroscopy

    Science.gov (United States)

    Magnuson, Martin; Schmidt, Susann; Hultman, Lars; Högberg, Hans

    2017-11-01

    The electronic structure and chemical bonding in reactively magnetron sputtered Zr Hx (x =0.15 , 0.30, 1.16) thin films with oxygen content as low as 0.2 at.% are investigated by 4d valence band, shallow 4p core-level, and 3d core-level x-ray photoelectron spectroscopy. With increasing hydrogen content, we observe significant reduction of the 4d valence states close to the Fermi level as a result of redistribution of intensity toward the H 1s-Zr 4d hybridization region at ˜6 eV below the Fermi level. For low hydrogen content (x =0.15 , 0.30), the films consist of a superposition of hexagonal closest-packed metal (α phase) and understoichiometric δ -Zr Hx (Ca F2 -type structure) phases, while for x =1.16 , the films form single-phase Zr Hx that largely resembles that of stoichiometric δ -Zr H2 phase. We show that the cubic δ -Zr Hx phase is metastable as thin film up to x =1.16 , while for higher H contents the structure is predicted to be tetragonally distorted. For the investigated Zr H1.16 film, we find chemical shifts of 0.68 and 0.51 eV toward higher binding energies for the Zr 4 p3 /2 and 3 d5 /2 peak positions, respectively. Compared to the Zr metal binding energies of 27.26 and 178.87 eV, this signifies a charge transfer from Zr to H atoms. The change in the electronic structure, spectral line shapes, and chemical shifts as a function of hydrogen content is discussed in relation to the charge transfer from Zr to H that affects the conductivity by charge redistribution in the valence band.

  5. Controlling the conduction band offset for highly efficient ZnO nanorods based perovskite solar cell

    International Nuclear Information System (INIS)

    Dong, Juan; Shi, Jiangjian; Li, Dongmei; Luo, Yanhong; Meng, Qingbo

    2015-01-01

    The mechanism of charge recombination at the interface of n-type electron transport layer (n-ETL) and perovskite absorber on the carrier properties in the perovskite solar cell is theoretically studied. By solving the one dimensional diffusion equation with different boundary conditions, it reveals that the interface charge recombination in the perovskite solar cell can be suppressed by adjusting the conduction band offset (ΔE C ) at ZnO ETL/perovskite absorber interface, thus leading to improvements in cell performance. Furthermore, Mg doped ZnO nanorods ETL has been designed to control the energy band levels. By optimizing the doping amount of Mg, the conduction band minimum of the Mg doped ZnO ETL has been raised up by 0.29 eV and a positive ΔE C of about 0.1 eV is obtained. The photovoltage of the cell is thus significantly increased due to the relatively low charge recombination

  6. Reduced energy offset via substitutional doping for efficient organic/inorganic hybrid solar cells.

    Science.gov (United States)

    Jin, Xiao; Sun, Weifu; Zhang, Qin; Ruan, Kelian; Cheng, Yuanyuan; Xu, Haijiao; Xu, Zhongyuan; Li, Qinghua

    2015-06-01

    Charge carrier transport in bulk heterojunction that is central to the device performance of solar cells is sensitively dependent on the energy level alignment of acceptor and donor. However, the effect of energy level regulation induced by nickel ions on the primary photoexcited electron transfer and the performance of P3HT/TiO2 hybrid solar cells remains being poorly understood and rarely studied. Here we demonstrate that the introduction of the versatile nickel ions into TiO2 nanocrystals can significantly elevate the conduction and valence band energy levels of the acceptor, thus resulting in a remarkable reduction of energy level offset between the conduction band of acceptor and lowest unoccupied molecular orbital of donor. By applying transient photoluminescence and femtosecond transient absorption spectroscopies, we demonstrate that the electron transfer becomes more competitive after incorporating nickel ions. In particular, the electron transfer life time is shortened from 30.2 to 16.7 ps, i.e., more than 44% faster than pure TiO2 acceptor, thus leading to a notable increase of power conversion efficiency in organic/inorganic hybrid solar cells. This work underscores the promising virtue of engineering the reduction of 'excess' energy offset to accelerate electron transport and demonstrates the potential of nickel ions in applications of solar energy conversion and photon detectors.

  7. Resonant photoemission at core-level shake-up thresholds: Valence-band satellites in nickel

    International Nuclear Information System (INIS)

    Bjoerneholm, O.; Andersen, J.N.; Wigren, C.; Nilsson, A.; Nyholm, R.; Ma; Ortensson, N.

    1990-01-01

    Three-hole satellites (3d 7 final-state configuration) in the nickel valence-band photoelectron spectrum have been identified at 13 and 18 eV binding energy with use of synchrotron radiation from the MAX storage ring. The three-hole satellites show resonances at photon energies close to the threshold for excitation of 3p 5 3d 9 core-hole shake-up states. The 13-eV satellite also shows a resonance directly at the 3p threshold. This is interpreted as an interference between the direct three-hole ionization and a shake-up transition in the Auger decay of the 3p hole. This shake-up process is also identified directly in the M 2,3 M 4,5 M 4,5 Auger spectrum

  8. Valence band structures of InAs/GaAs quantum rings using the Fourier transform method

    International Nuclear Information System (INIS)

    Jia Boyong; Yu Zhongyuan; Liu Yumin

    2009-01-01

    The valence band structures of strained InAs/GaAs quantum rings are calculated, with the four-band k · p model, in the framework of effective-mass envelope function theory. When determining the Hamiltonian matrix elements, we develop the Fourier transform method instead of the widely used analytical integral method. Using Fourier transform, we have investigated the energy levels as functions of the geometrical parameters of the rings and compared our results with those obtained by the analytical integral method. The results show that the energy levels in the quantum rings change dramatically with the inner radius, outer radius, average radius, width, height of the ring and the distance between two adjacent rings. Our method can be adopted in low-dimensional structures with arbitrary shape. Our results are consistent with those in the literature and should be helpful for studying and fabricating optoelectronic devices

  9. Band alignment of ZnO/multilayer MoS{sub 2} interface determined by x-ray photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Xinke, E-mail: xkliu@szu.edu.cn, E-mail: liuwj@szu.edu.cn; He, Jiazhu; Chen, Le; Li, Kuilong; Jia, Fang; Zeng, Yuxiang; Lu, Youming; Zhu, Deliang; Liu, Wenjun, E-mail: xkliu@szu.edu.cn, E-mail: liuwj@szu.edu.cn [College of Materials Science and Engineering, Nanshan District Key Lab for Biopolymer and Safety Evaluation, Shenzhen University, 3688 Nanhai Ave, Shenzhen 518060 (China); Zhang, Yuan [School of Physics and Electronic Information, Hua Bei Normal University, 100 Dongshan Road, Huai Bei 235000 (China); Liu, Qiang; Yu, Wenjie [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, CAS, 865 Chang Ning Road, Shanghai 200050 (China); Wu, Jing [Institute of Materials research and Engineering (IMRE), 2 Fusionopolis Way, Innovis, #08-03, 138634 Singapore (Singapore); He, Zhubing [Department of Materials Science and Engineering, South University of Science and Technology of China, 1088 Xueyuan Road, Shenzhen 518055 (China); Ang, Kah-Wee [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117583 Singapore (Singapore)

    2016-08-15

    The energy band alignment between ZnO and multilayer (ML)-MoS{sub 2} was characterized using high-resolution x-ray photoelectron spectroscopy. The ZnO film was deposited using an atomic layer deposition tool, and ML-MoS{sub 2} was grown by chemical vapor deposition. A valence band offset (VBO) of 3.32 eV and a conduction band offset (CBO) of 1.12 eV were obtained for the ZnO/ML-MoS{sub 2} interface without any treatment. With CHF{sub 3} plasma treatment, a VBO and a CBO across the ZnO/ML-MoS{sub 2} interface were found to be 3.54 eV and 1.34 eV, respectively. With the CHF{sub 3} plasma treatment, the band alignment of the ZnO/ML-MoS{sub 2} interface has been changed from type II or staggered band alignment to type III or misaligned one, which favors the electron-hole pair separation. The band alignment difference is believed to be dominated by the down-shift in the core level of Zn 2p or the interface dipoles, which is caused by the interfacial layer rich in F.

  10. Effects of surface condition on the work function and valence-band position of ZnSnN2

    Science.gov (United States)

    Shing, Amanda M.; Tolstova, Yulia; Lewis, Nathan S.; Atwater, Harry A.

    2017-12-01

    ZnSnN2 is an emerging wide band gap earth-abundant semiconductor with potential applications in photonic devices such as solar cells, LEDs, and optical sensors. We report the characterization by ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy of reactively radio-frequency sputtered II-IV-nitride ZnSnN2 thin films. For samples transferred in high vacuum, the ZnSnN2 surface work function was 4.0 ± 0.1 eV below the vacuum level, with a valence-band onset of 1.2 ± 0.1 eV below the Fermi level. The resulting band diagram indicates that the degenerate bulk Fermi level position in ZnSnN2 shifts to mid-gap at the surface due to band bending that results from equilibration with delocalized surface states within the gap. Brief (< 10 s) exposures to air, a nitrogen-plasma treatment, or argon-ion sputtering caused significant chemical changes at the surface, both in surface composition and interfacial energetics. The relative band positioning of the n-type semiconductor against standard redox potentials indicated that ZnSnN2 has an appropriate energy band alignment for use as a photoanode to effect the oxygen-evolution reaction.

  11. Band alignment of atomic layer deposited MgO/Zn0.8Al0.2O heterointerface determined by charge corrected X-ray photoelectron spectroscopy

    Science.gov (United States)

    Yan, Baojun; Liu, Shulin; Yang, Yuzhen; Heng, Yuekun

    2016-05-01

    Pure magnesium (MgO) and zinc oxide doped with aluminum oxide (Zn0.8Al0.2O) were prepared via atomic layer deposition. We have studied the structure and band gap of bulk Zn0.8Al0.2O material by X-ray diffractometer (XRD) and Tauc method, and the band offsets and alignment of atomic layer deposited MgO/Zn0.8Al0.2O heterointerface were investigated systematically using X-ray photoelectron spectroscopy (XPS) in this study. Different methodologies, such as neutralizing electron gun, the use of C 1s peak recalibration and zero charging method, were applied to recover the actual position of the core levels in insulator materials which were easily influenced by differential charging phenomena. Schematic band alignment diagram, valence band offset (ΔEV) and conduction band offset (ΔEC) for the interface of the MgO/Zn0.8Al0.2O heterostructure have been constructed. An accurate value of ΔEV = 0.72 ± 0.11 eV was obtained from various combinations of core levels of heterojunction with varied MgO thickness. Given the experimental band gaps of 7.83 eV for MgO and 5.29 eV for Zn0.8Al0.2O, a type-II heterojunction with a ΔEC of 3.26 ± 0.11 eV was found. Band offsets and alignment studies of these heterojunctions are important for gaining deep consideration to the design of various optoelectronic devices based on such heterointerface.

  12. Energy shift and conduction-to-valence band transition mediated by a time-dependent potential barrier in graphene

    Science.gov (United States)

    Chaves, Andrey; da Costa, D. R.; de Sousa, G. O.; Pereira, J. M.; Farias, G. A.

    2015-09-01

    We investigate the scattering of a wave packet describing low-energy electrons in graphene by a time-dependent finite-step potential barrier. Our results demonstrate that, after Klein tunneling through the barrier, the electron acquires an extra energy which depends on the rate of change of the barrier height with time. If this rate is negative, the electron loses energy and ends up as a valence band state after leaving the barrier, which effectively behaves as a positively charged quasiparticle.

  13. Simultaneous Conduction and Valence Band Quantization in Ultrashallow High-Density Doping Profiles in Semiconductors

    Science.gov (United States)

    Mazzola, F.; Wells, J. W.; Pakpour-Tabrizi, A. C.; Jackman, R. B.; Thiagarajan, B.; Hofmann, Ph.; Miwa, J. A.

    2018-01-01

    We demonstrate simultaneous quantization of conduction band (CB) and valence band (VB) states in silicon using ultrashallow, high-density, phosphorus doping profiles (so-called Si:P δ layers). We show that, in addition to the well-known quantization of CB states within the dopant plane, the confinement of VB-derived states between the subsurface P dopant layer and the Si surface gives rise to a simultaneous quantization of VB states in this narrow region. We also show that the VB quantization can be explained using a simple particle-in-a-box model, and that the number and energy separation of the quantized VB states depend on the depth of the P dopant layer beneath the Si surface. Since the quantized CB states do not show a strong dependence on the dopant depth (but rather on the dopant density), it is straightforward to exhibit control over the properties of the quantized CB and VB states independently of each other by choosing the dopant density and depth accordingly, thus offering new possibilities for engineering quantum matter.

  14. Valence band structure and density of states effective mass model of biaxial tensile strained silicon based on k · p theory

    International Nuclear Information System (INIS)

    Kuang Qian-Wei; Liu Hong-Xia; Wang Shu-Long; Qin Shan-Shan; Wang Zhi-Lin

    2011-01-01

    After constructing a stress and strain model, the valence bands of in-plane biaxial tensile strained Si is calculated by k · p method. In the paper we calculate the accurate anisotropy valance bands and the splitting energy between light and heavy hole bands. The results show that the valance bands are highly distorted, and the anisotropy is more obvious. To obtain the density of states (DOS) effective mass, which is a very important parameter for device modeling, a DOS effective mass model of biaxial tensile strained Si is constructed based on the valance band calculation. This model can be directly used in the device model of metal—oxide semiconductor field effect transistor (MOSFET). It also a provides valuable reference for biaxial tensile strained silicon MOSFET design. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  15. Band-Bending of Ga-Polar GaN Interfaced with Al2O3 through Ultraviolet/Ozone Treatment.

    Science.gov (United States)

    Kim, Kwangeun; Ryu, Jae Ha; Kim, Jisoo; Cho, Sang June; Liu, Dong; Park, Jeongpil; Lee, In-Kyu; Moody, Baxter; Zhou, Weidong; Albrecht, John; Ma, Zhenqiang

    2017-05-24

    Understanding the band bending at the interface of GaN/dielectric under different surface treatment conditions is critically important for device design, device performance, and device reliability. The effects of ultraviolet/ozone (UV/O 3 ) treatment of the GaN surface on the energy band bending of atomic-layer-deposition (ALD) Al 2 O 3 coated Ga-polar GaN were studied. The UV/O 3 treatment and post-ALD anneal can be used to effectively vary the band bending, the valence band offset, conduction band offset, and the interface dipole at the Al 2 O 3 /GaN interfaces. The UV/O 3 treatment increases the surface energy of the Ga-polar GaN, improves the uniformity of Al 2 O 3 deposition, and changes the amount of trapped charges in the ALD layer. The positively charged surface states formed by the UV/O 3 treatment-induced surface factors externally screen the effect of polarization charges in the GaN, in effect, determining the eventual energy band bending at the Al 2 O 3 /GaN interfaces. An optimal UV/O 3 treatment condition also exists for realizing the "best" interface conditions. The study of UV/O 3 treatment effect on the band alignments at the dielectric/III-nitride interfaces will be valuable for applications of transistors, light-emitting diodes, and photovoltaics.

  16. Structural, electronic structure, and band alignment properties at epitaxial NiO/Al{sub 2}O{sub 3} heterojunction evaluated from synchrotron based X-ray techniques

    Energy Technology Data Exchange (ETDEWEB)

    Singh, S. D., E-mail: devsh@rrcat.gov.in; Das, Arijeet; Ajimsha, R. S.; Upadhyay, Anuj; Kamparath, Rajiv; Mukherjee, C.; Misra, P.; Rai, S. K.; Sinha, A. K.; Ganguli, Tapas [Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013 (India); Nand, Mangla; Jha, S. N. [Bhabha Atomic Research Centre, Mumbai, Maharashtra 400085 (India); Shukla, D. K.; Phase, D. M. [UGC-DAE Consortium for Scientific Research, Khandwa Road, Indore, Madhya Pradesh 452017 (India)

    2016-04-28

    The valence band offset value of 2.3 ± 0.2 eV at epitaxial NiO/Al{sub 2}O{sub 3} heterojunction is determined from photoelectron spectroscopy experiments. Pulsed laser deposited thin film of NiO on Al{sub 2}O{sub 3} substrate is epitaxially grown along [111] direction with two domain structures, which are in-plane rotated by 60° with respect to each other. Observation of Pendellosung oscillations around Bragg peak confirms high interfacial and crystalline quality of NiO layer deposited on Al{sub 2}O{sub 3} substrate. Surface related feature in Ni 2p{sub 3/2} core level spectra along with oxygen K-edge soft X-ray absorption spectroscopy results indicates that the initial growth of NiO on Al{sub 2}O{sub 3} substrate is in the form of islands, which merge to form NiO layer for the larger coverage. The value of conduction band offset is also evaluated from the measured values of band gaps of NiO and Al{sub 2}O{sub 3} layers. A type-I band alignment at NiO and Al{sub 2}O{sub 3} heterojunction is also obtained. The determined values of band offsets can be useful in heterojunction based light emitting devices.

  17. Band alignment of HfO{sub 2}/multilayer MoS{sub 2} interface determined by x-ray photoelectron spectroscopy: Effect of CHF{sub 3} treatment

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Xinke; He, Jiazhu; Tang, Dan; Jia, Fang; Lu, Youming, E-mail: ymlu@szu.edu.cn; Zhu, Deliang; Liu, Wenjun; Cao, Peijiang; Han, Sun [College of Materials Science and Engineering, Shenzhen Engineering Laboratory for Advanced Technology of Ceramics, Nanshan District Key Lab for Biopolymer and Safety Evaluation, Shenzhen University, 3688 Nanhai Ave, Shenzhen 518060 (China); Liu, Qiang; Wen, Jiao; Yu, Wenjie, E-mail: casan@mail.sim.ac.cn [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, CAS,865 Chang Ning Road, Shanghai 200050 (China); Pan, Jisheng [Institute of Materials Research and Engineering, Agency for Science Technology and Research, Singapore 117602 (Singapore); He, Zhubing [Department of Materials Science and Engineering, South University of Science and Technology of China, 1088 Xueyuan Road, Shenzhen 518055 (China); Ang, Kah-Wee [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117583 (Singapore)

    2015-09-07

    The energy band alignment between HfO{sub 2}/multilayer (ML)-MoS{sub 2} was characterized using high-resolution x-ray photoelectron spectroscopy. The HfO{sub 2} was deposited using an atomic layer deposition tool, and ML-MoS{sub 2} was grown by chemical vapor deposition. A valence band offset (VBO) of 1.98 eV and a conduction band offset (CBO) of 2.72 eV were obtained for the HfO{sub 2}/ML-MoS{sub 2} interface without any treatment. With CHF{sub 3} plasma treatment, a VBO and a CBO across the HfO{sub 2}/ML-MoS{sub 2} interface were found to be 2.47 eV and 2.23 eV, respectively. The band alignment difference is believed to be dominated by the down-shift in the core level of Hf 4d and up-shift in the core level of Mo 3d, or the interface dipoles, which caused by the interfacial layer in rich of F.

  18. Valence band electronic structure and band alignment of LaAlO{sub 3}/SrTiO{sub 3}(111) heterointerfaces

    Energy Technology Data Exchange (ETDEWEB)

    Gabel, J.; Scheiderer, P.; Zapf, M.; Schuetz, P.; Sing, M.; Claessen, R. [Physikalisches Institut and Roentgen Center for Complex Material Systems (RCCM), Universitaet Wuerzburg (Germany); Schlueter, C.; Lee, T.L. [Diamond Light Source, Didcot (United Kingdom)

    2015-07-01

    As in the famous LaAlO{sub 3}(LAO)/SrTiO{sub 3}(STO) (001) a two-dimensional electron system (2DES) also forms at the interface between LAO and STO in (111) orientation. A distinct feature of the (111) interface is its peculiar real space topology. Each bilayer represents a buckled honeycomb lattice similar to graphene which is known theoretically to host various topologically non-trivial states. Bilayer STO in proximity to the interface can be regarded as a three-orbital generalization of graphene with enhanced electron correlations making it a promising candidate for the realization of strongly correlated topological phases. We have investigated the electronic structure of the LAO/STO (111) heterostructure in relation to the oxygen vacancy concentration which we can control by synchrotron light irradiation and oxygen dosing. With hard X-ray photoemission we study the core levels, whereas resonant soft X-ray photoemission is used to probe the interfacial valence band (VB) states. Two VB features are found: a peak at the Fermi level associated with the 2DES and in-gap states at higher binding energies attributed to oxygen vacancies. By varying the oxygen vacancy contribution we can tune the emergence of the VB states and engineer the interfacial band alignment.

  19. Band alignment in visible-light photo-active CoO/SrTiO{sub 3} (001) heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Seo, Hosung; Demkov, Alexander A., E-mail: demkov@physics.utexas.edu [Department of Physics, The University of Texas at Austin, Austin, Texas 78712 (United States)

    2014-12-28

    Epitaxial oxide heterostructures are of fundamental interest in a number of problems ranging from oxide electronics to model catalysts. The epitaxial CoO/SrTiO{sub 3} (001) heterostructure on Si(001) has been recently studied as a model oxide catalyst for water splitting under visible light irradiation (Ngo et al., J. Appl. Phys. 114, 084901 (2013)). We use density functional theory to investigate the valence band offset at the CoO/SrTiO{sub 3} (001) interface. We examine the mechanism of charge transfer and dielectric screening at the interface and demonstrate that charge transfer is mediated by the metal-induced gap states in SrTiO{sub 3}, while the dielectric screening at the interface is largely governed by the ionic polarization of under-coordinated oxygen. Based on this finding, we argue that strain relaxation in CoO plays a critical role in determining the band offset. We find that the offsets of 1.36–1.10 eV, calculated in the Schottky-limit are in excellent agreement with the experimental value of 1.20 eV. In addition, we investigate the effect of the Hubbard correction, applied on the Co 3d states, on the dipole layer and potential shift at the interface.

  20. Valence instabilities as a source of actinide system inconsistencies

    International Nuclear Information System (INIS)

    Sandenaw, T.A.

    1979-01-01

    Light actinide elements alone, and in some of their alloys, may exist as a static or dynamic mixture of two configurations. Such a state can explain both a resistivity maximum and lack of magnetic order observed in so many actinide materials, and still be compatible with the existence of f-electrons in narrow bands. Impurity elements may stabilize slightly different intermediate valence states in U, Np, and Pu, thus contributing to inconsistencies in published results. The physical property behavior of mixed-valence, rare-earth compounds is very much like that observed in development of antiphase (martensitic) structures. Martensitic transformations in U, Np, and Pu, from high-temperature b. c. c. to alpha phase, may be a way of ordering an alloy-like metal of mixed or intermediate valence. The relative stability of each phase structure may depend upon its electron-valence ratio. A Hubbard model for electron correlations in a narrow energy band has been invoked in most recent theories for explaining light actinide behavior. Such a model may also be applicable to crystal symmetry changes in martensitic transformations in actinides

  1. Photoluminescence and Band Alignment of Strained GaAsSb/GaAs QW Structures Grown by MBE on GaAs

    Directory of Open Access Journals (Sweden)

    Nigamananda Samal

    2010-02-01

    Full Text Available An in-depth optimization of growth conditions and investigation of optical properties including discussions on band alignment of GaAsSb/GaAs quantum well (QW on GaAs by molecular beam epitaxy (MBE are reported. Optimal MBE growth temperature of GaAsSb QW is found to be 470 ± 10 °C. GaAsSb/GaAs QW with Sb content ~0.36 has a weak type-II band alignment with valence band offset ratio QV ~1.06. A full width at half maximum (FWHM of ~60 meV in room temperature (RT photoluminescence (PL indicates fluctuation in electrostatic potential to be less than 20 meV. Samples grown under optimal conditions do not exhibit any blue shift of peak in RT PL spectra under varying excitation.

  2. Defect induced structural inhomogeneity, ultraviolet light emission and near-band-edge photoluminescence broadening in degenerate In2O3 nanowires

    Science.gov (United States)

    Mukherjee, Souvik; Sarkar, Ketaki; Wiederrecht, Gary P.; Schaller, Richard D.; Gosztola, David J.; Stroscio, Michael A.; Dutta, Mitra

    2018-04-01

    We demonstrate here defect induced changes on the morphology and surface properties of indium oxide (In2O3) nanowires and further study their effects on the near-band-edge (NBE) emission, thereby showing the significant influence of surface states on In2O3 nanostructure based device characteristics for potential optoelectronic applications. In2O3 nanowires with cubic crystal structure (c-In2O3) were synthesized via carbothermal reduction technique using a gold-catalyst-assisted vapor-liquid-solid method. Onset of strong optical absorption could be observed at energies greater than 3.5 eV consistent with highly n-type characteristics due to unintentional doping from oxygen vacancy ({V}{{O}}) defects as confirmed using Raman spectroscopy. A combination of high resolution transmission electron microscopy, x-ray photoelectron spectroscopy and valence band analysis on the nanowire morphology and stoichiometry reveals presence of high-density of {V}{{O}} defects on the surface of the nanowires. As a result, chemisorbed oxygen species can be observed leading to upward band bending at the surface which corresponds to a smaller valence band offset of 2.15 eV. Temperature dependent photoluminescence (PL) spectroscopy was used to study the nature of the defect states and the influence of the surface states on the electronic band structure and NBE emission has been discussed. Our data reveals significant broadening of the NBE PL peak consistent with impurity band broadening leading to band-tailing effect from heavy doping.

  3. Large shift and small broadening of Br2 valence band upon dimer formation with H2O: an ab initio study.

    Science.gov (United States)

    Franklin-Mergarejo, Ricardo; Rubayo-Soneira, Jesus; Halberstadt, Nadine; Ayed, Tahra; Bernal-Uruchurtu, Margarita I; Hernández-Lamoneda, Ramón; Janda, Kenneth C

    2011-06-16

    Valence electronic excitation spectra are calculated for the H(2)O···Br(2) complex using highly correlated ab initio potentials for both the ground and the valence electronic excited states and a 2-D approximation for vibrational motion. Due to the strong interaction between the O-Br and the Br-Br stretching motions, inclusion of these vibrations is the minimum necessary for the spectrum calculation. A basis set calculation is performed to determine the vibrational wave functions for the ground electronic state and a wave packet simulation is conducted for the nuclear dynamics on the excited state surfaces. The effects of both the spin-orbit interaction and temperature on the spectra are explored. The interaction of Br(2) with a single water molecule induces nearly as large a shift in the spectrum as is observed for an aqueous solution. In contrast, complex formation has a remarkably small effect on the T = 0 K width of the valence bands due to the fast dissociation of the dihalogen bond upon excitation. We therefore conclude that the widths of the spectra in aqueous solution are mostly due to inhomogeneous broadening. © 2011 American Chemical Society

  4. Decoding emotional valence from electroencephalographic rhythmic activity.

    Science.gov (United States)

    Celikkanat, Hande; Moriya, Hiroki; Ogawa, Takeshi; Kauppi, Jukka-Pekka; Kawanabe, Motoaki; Hyvarinen, Aapo

    2017-07-01

    We attempt to decode emotional valence from electroencephalographic rhythmic activity in a naturalistic setting. We employ a data-driven method developed in a previous study, Spectral Linear Discriminant Analysis, to discover the relationships between the classification task and independent neuronal sources, optimally utilizing multiple frequency bands. A detailed investigation of the classifier provides insight into the neuronal sources related with emotional valence, and the individual differences of the subjects in processing emotions. Our findings show: (1) sources whose locations are similar across subjects are consistently involved in emotional responses, with the involvement of parietal sources being especially significant, and (2) even though the locations of the involved neuronal sources are consistent, subjects can display highly varying degrees of valence-related EEG activity in the sources.

  5. Effect of oxygen on tuning the TiNx metal gate work function on LaLuO3

    International Nuclear Information System (INIS)

    Mitrovic, I.Z.; Przewlocki, H.M.; Piskorski, K.; Simutis, G.; Dhanak, V.R.; Sedghi, N.; Hall, S.

    2012-01-01

    This paper presents experimental evidence on effective work function tuning due to the presence of oxygen at the TiNx/LaLuO 3 interface. Two complementary techniques, internal photoemission and X-ray photoelectron spectroscopy, show good agreement on the position of the metal gate Fermi level to conduction (2.79 ± 0.25 eV) and valence (2.65 ± 0.08 eV) band edge for TiNx/bulk LaLuO 3 gate stacks. The chemical shifts of Ti2p and N1s core levels and different degree in ionicity of TiNx metal gates correlate with the observed valence band offset shifts. The results have significance for setting the band edge work function and resulting low threshold voltage for ultimately scaled LaLuO 3 -based p-metal oxide semiconductor field effect transistor devices. - Highlights: ► The conduction band offset measured by internal photoemission. ► The valence band offset (VBO) measured by X-ray photoelectron spectroscopy. ► Different degree in ionicity of TiNx correlates with the VBO shifts. ► The effective work function of the gate stacks varies from 4.6 to 5.2 eV. ► Oxygen at the TiNx/LaLuO 3 interface increases effective work function.

  6. Defect induced structural inhomogeneity, ultraviolet light emission and near-band-edge photoluminescence broadening in degenerate In 2 O 3 nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Mukherjee, Souvik; Sarkar, Ketaki; Wiederrecht, Gary P.; Schaller, Richard D.; Gosztola, David J.; Stroscio, Michael A.; Dutta, Mitra

    2018-03-01

    We demonstrate here defect induced changes on the morphology and surface properties of indium oxide (In2O3) nanowires and further study their effects on the near-band-edge (NBE) emission, thereby showing the significant influence of surface states on In2O3 nanostructure based device characteristics for potential optoelectronic applications. In2O3 nanowires with cubic crystal structure (c-In2O3) were synthesized via carbothermal reduction technique using a gold-catalyst-assisted vapor–liquid–solid method. Onset of strong optical absorption could be observed at energies greater than 3.5 eV consistent with highly n-type characteristics due to unintentional doping from oxygen vacancy (VO) defects as confirmed using Raman spectroscopy. A combination of high resolution transmission electron microscopy, x-ray photoelectron spectroscopy and valence band analysis on the nanowire morphology and stoichiometry reveals presence of high-density of VO defects on the surface of the nanowires. As a result, chemisorbed oxygen species can be observed leading to upward band bending at the surface which corresponds to a smaller valence band offset of 2.15 eV. Temperature dependent photoluminescence (PL) spectroscopy was used to study the nature of the defect states and the influence of the surface states on the electronic band structure and NBE emission has been discussed. Our data reveals significant broadening of the NBE PL peak consistent with impurity band broadening leading to band-tailing effect from heavy doping.

  7. ZnO epitaxy on SiC(0001-bar) substrate: Comparison with ZnO/SiC(0 0 0 1) heterostructure

    International Nuclear Information System (INIS)

    Ashrafi, Almamun; Aminuzzaman, Mohammod

    2011-01-01

    ZnO thin layers deposited on 6H-SiC substrates showed six-fold crystal symmetry with an epitaxial relationship of (0 0 0 2) ZnO ||(0 0 0 6) SiC and [112-bar 0] ZnO ||[112-bar 0] SiC . Despite the different 6H-SiC substrate surface orientations for the ZnO epitaxy, the orientation relationship of ZnO/6H-SiC heterostructures is identical, as confirmed by X-ray diffraction studies. In these ZnO/6H-SiC(0 0 0 1) and ZnO/6H-SiC(0001-bar) heterostructures, the valence band offsets are measured to be 1.12 eV and 1.09 eV, leading to the conduction band offset values of 0.75 eV and 0.72 eV, respectively. These slightly different band-offset values in ZnO/6H-SiC heterojunctions are attributed to the variation of valence band maximums and the different interface charge compensation mechanisms.

  8. Influence of LaSiOx passivation interlayer on band alignment between PEALD-Al2O3 and 4H-SiC determined by X-ray photoelectron spectroscopy

    Science.gov (United States)

    Wang, Qian; Cheng, Xinhong; Zheng, Li; Shen, Lingyan; Zhang, Dongliang; Gu, Ziyue; Qian, Ru; Cao, Duo; Yu, Yuehui

    2018-01-01

    The influence of lanthanum silicate (LaSiOx) passivation interlayer on the band alignment between plasma enhanced atomic layer deposition (PEALD)-Al2O3 films and 4H-SiC was investigated by high resolution X-ray photoelectron spectroscopy (XPS). An ultrathin in situ LaSiOx interfacial passivation layer (IPL) was introduced between the Al2O3 gate dielectric and the 4H-SiC substrate to enhance the interfacial characteristics. The valence band offset (VBO) and corresponding conduction band offset (CBO) for the Al2O3/4H-SiC interface without any passivation were extracted to be 2.16 eV and 1.49 eV, respectively. With a LaSiOx IPL, a VBO of 1.79 eV and a CBO of 1.86 eV could be obtained across the Al2O3/4H-SiC interface. The difference in the band alignments was dominated by the band bending or band shift in the 4H-SiC substrate as a result of different interfacial layers (ILs) formed at the interface. This understanding of the physical details of the band alignment could be a good foundation for Al2O3/LaSiOx/4H-SiC heterojunctions applied in the 4H-SiC metal-oxide-semiconductor field effect transistors (MOSFETs).

  9. Contributions of conduction band offset to the enhanced separation efficiency of photoinduced charges for SrTiO3/Bi2O3 heterojunction semiconductor

    International Nuclear Information System (INIS)

    Zhang, Zhenlong; Zhu, Jichun; Li, Shengjun; Mao, Yanli

    2014-01-01

    SrTiO 3 /Bi 2 O 3 heterojunction semiconductor was prepared and characterized by X-ray diffraction, UV–vis absorption spectrum, and scanning electron microscope, surface photovoltage spectroscopy, and photoluminescence spectroscopy. The surface photovoltage spectra indicate that the separation efficiency of photoinduced charges for SrTiO 3 /Bi 2 O 3 was enhanced compared with that of SrTiO 3 or Bi 2 O 3 . The energy band diagram of SrTiO 3 /Bi 2 O 3 heterojunction was directly determined with X-ray photoelectron spectroscopy, and the conduction band offset between SrTiO 3 and Bi 2 O 3 was quantified to be 0.28±0.03 eV. The photoluminescence spectra display that the recombination rate of photoinduced carriers for SrTiO 3 /Bi 2 O 3 decreases compared with that of SrTiO 3 or Bi 2 O 3 , which is mainly due to the energy levels matching between them. Therefore the enhanced separation efficiency of photoinduced charges is resulting from the energy difference between the conduction band edges of SrTiO 3 and Bi 2 O 3 . -- Graphical abstract: Enhanced separation efficiency for SrTiO 3 /Bi 2 O 3 is resulting from the energy difference between the conduction band edges. Highlights: ●Heterojunction semiconductor of SrTiO 3 /Bi 2 O 3 was prepared. ●SrTiO 3 /Bi 2 O 3 presents enhanced separation efficiency. ●Conduction band offset between SrTiO 3 and Bi 2 O 3 is quantified. ●Recombination rate of SrTiO 3 /Bi 2 O 3 decreases compared with single phases

  10. Attractive electron correlation in wide band gap semiconductors by electron-photon interaction

    International Nuclear Information System (INIS)

    Takeda, Hiroyuki; Yoshino, Katsumi

    2004-01-01

    We theoretically demonstrate attractive electron correlation in wide band gap semiconductors by electron-photon interaction. At low temperature, wavevectors of electromagnetic waves absorbed in wide band gap semiconductors cannot be neglected for wavevectors of electron waves; that is, electromagnetic waves affect the movements of electrons. In particular, attractive interaction occurs between two electrons when one electron changes from a valence band to a conduction band and the other electron changes from a conduction band to a valence band

  11. A study of the valence shell electronic states of s-triazine by photoabsorption spectroscopy and ab initio calculations

    Energy Technology Data Exchange (ETDEWEB)

    Holland, D.M.P., E-mail: david.holland@stfc.ac.uk [Daresbury Laboratory, Daresbury, Warrington, Cheshire WA4 4AD (United Kingdom); Shaw, D.A. [Daresbury Laboratory, Daresbury, Warrington, Cheshire WA4 4AD (United Kingdom); Stener, M.; Decleva, P. [Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Trieste, Via L. Giorgieri, I-34127 Trieste (Italy); Consorzio Interuniversitario Nazionale per la Scienze e Tecnologia dei Materiali, INSTM, Unità di Trieste (Italy); CNR-IOM, Trieste (Italy); Coriani, S. [Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Trieste, Via L. Giorgieri, I-34127 Trieste (Italy); Consorzio Interuniversitario Nazionale per la Scienze e Tecnologia dei Materiali, INSTM, Unità di Trieste (Italy); Aarhus Institute of Advanced Studies, Aarhus University, 8000 Aarhus C (Denmark)

    2016-09-30

    Highlights: • The valence shell photoabsorption spectrum of s-triazine has been measured. • Electronic structure calculated with TDDFT and coupled cluster approaches. • Assignments proposed for Rydberg and valence states. • Mixing between Rydberg and valence states important. - Abstract: The absolute photoabsorption cross section of s-triazine has been measured between 4 and 40 eV, and is dominated by bands associated with valence states. Structure due to Rydberg excitations is both weak and irregular. Jahn-Teller interactions affect the vibronic structure observed in the Rydberg absorption bands due to excitation from the 1e″ or 6e′ orbitals. The interpretation of the experimental spectrum has been guided by transition energies and oscillator strengths, for Rydberg and valence states, calculated with the time-dependent version of density functional theory and with the coupled cluster linear response approach. The theoretical studies indicate that Rydberg/Rydberg and Rydberg/valence mixing is important.

  12. Determination of conduction and valence band electronic structure ...

    Indian Academy of Sciences (India)

    shifts in the rutile Ti d-band to lower energy with respect to anatase, i.e., ... requires excitation with UV light due to its wide band ... RIXS maps were compared to the theoretical results .... optical methods are insufficient, such as dark samples.

  13. ZnO epitaxy on SiC(0001-bar) substrate: Comparison with ZnO/SiC(0 0 0 1) heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    Ashrafi, Almamun, E-mail: ash2phy@gmail.com [Department of Physics, University of Vermont, VT 05405 (United States); Aminuzzaman, Mohammod [Department of Chemical Science, Universiti Tunku Abdul Rahman, Perak (Malaysia)

    2011-05-01

    ZnO thin layers deposited on 6H-SiC substrates showed six-fold crystal symmetry with an epitaxial relationship of (0 0 0 2){sub ZnO}||(0 0 0 6){sub SiC} and [112-bar 0]{sub ZnO}||[112-bar 0]{sub SiC}. Despite the different 6H-SiC substrate surface orientations for the ZnO epitaxy, the orientation relationship of ZnO/6H-SiC heterostructures is identical, as confirmed by X-ray diffraction studies. In these ZnO/6H-SiC(0 0 0 1) and ZnO/6H-SiC(0001-bar) heterostructures, the valence band offsets are measured to be 1.12 eV and 1.09 eV, leading to the conduction band offset values of 0.75 eV and 0.72 eV, respectively. These slightly different band-offset values in ZnO/6H-SiC heterojunctions are attributed to the variation of valence band maximums and the different interface charge compensation mechanisms.

  14. Ultrawide band gap amorphous oxide semiconductor, Ga–Zn–O

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Junghwan, E-mail: JH.KIM@lucid.msl.titech.ac.jp [Materials and Structures Laboratory, Tokyo Institute of Technology, Mailbox R3-4, 4259 Nagatsuta, Midori-ku, Yokohama (Japan); Miyokawa, Norihiko; Sekiya, Takumi; Ide, Keisuke [Materials and Structures Laboratory, Tokyo Institute of Technology, Mailbox R3-4, 4259 Nagatsuta, Midori-ku, Yokohama (Japan); Toda, Yoshitake [Materials Research Center for Element Strategy, Tokyo Institute of Technology, Mailbox SE-6, 4259 Nagatsuta, Midori-ku, Yokohama (Japan); Hiramatsu, Hidenori; Hosono, Hideo; Kamiya, Toshio [Materials and Structures Laboratory, Tokyo Institute of Technology, Mailbox R3-4, 4259 Nagatsuta, Midori-ku, Yokohama (Japan); Materials Research Center for Element Strategy, Tokyo Institute of Technology, Mailbox SE-6, 4259 Nagatsuta, Midori-ku, Yokohama (Japan)

    2016-09-01

    We fabricated amorphous oxide semiconductor films, a-(Ga{sub 1–x}Zn{sub x})O{sub y}, at room temperature on glass, which have widely tunable band gaps (E{sub g}) ranging from 3.47–4.12 eV. The highest electron Hall mobility ~ 7 cm{sup 2} V{sup −1} s{sup −1} was obtained for E{sub g} = ~ 3.8 eV. Ultraviolet photoemission spectroscopy revealed that the increase in E{sub g} with increasing the Ga content comes mostly from the deepening of the valence band maximum level while the conduction band minimum level remains almost unchanged. These characteristics are explained by their electronic structures. As these films can be fabricated at room temperature on plastic, this achievement extends the applications of flexible electronics to opto-electronic integrated circuits associated with deep ultraviolet region. - Highlights: • Incorporation of H/H{sub 2}O stabilizes the amorphous phase. • Ultrawide band gap (~ 3.8 eV) amorphous oxide semiconductor was fabricated. • The increase in band gap comes mostly from the deepening of the valence band maximum level. • Donor level is more likely aligned to the valence band maximum level.

  15. Modified band alignment effect in ZnO/Cu2O heterojunction solar cells via Cs2O buffer insertion

    Science.gov (United States)

    Eom, Kiryung; Lee, Dongyoon; Kim, Seunghwan; Seo, Hyungtak

    2018-02-01

    The effects of a complex buffer layer of cesium oxide (Cs2O) on the photocurrent response in oxide heterojunction solar cells (HSCs) were investigated. A p-n junction oxide HSC was fabricated using p-type copper (I) oxide (Cu2O) and n-type zinc oxide (ZnO); the buffer layer was inserted between the Cu2O and fluorine-doped tin oxide (FTO). Ultraviolet-visible (UV-vis) and x-ray and ultraviolet photoelectron spectroscopy analyses were performed to characterize the electronic band structures of cells, both with and without this buffer layer. In conjunction with the measured band electronic structures, the significantly improved visible-range photocurrent spectra of the buffer-inserted HSC were analyzed in-depth. As a result, the 1 sun power conversion efficiency was increased by about three times by the insertion of buffer layer. The physicochemical origin of the photocurrent enhancement was mainly ascribed to the increased photocarrier density in the buffer layer and modified valence band offset to promote the effective hole transfer at the interface to FTO on the band-alignment model.

  16. Valence holes observed in nanodiamonds dispersed in water

    Science.gov (United States)

    Petit, Tristan; Pflüger, Mika; Tolksdorf, Daniel; Xiao, Jie; Aziz, Emad F.

    2015-02-01

    Colloidal dispersion is essential for most nanodiamond applications, but its influence on nanodiamond electronic properties remains unknown. Here we have probed the electronic structure of oxidized detonation nanodiamonds dispersed in water by using soft X-ray absorption and emission spectroscopies at the carbon and oxygen K edges. Upon dispersion in water, the π* transitions from sp2-hybridized carbon disappear, and holes in the valence band are observed.Colloidal dispersion is essential for most nanodiamond applications, but its influence on nanodiamond electronic properties remains unknown. Here we have probed the electronic structure of oxidized detonation nanodiamonds dispersed in water by using soft X-ray absorption and emission spectroscopies at the carbon and oxygen K edges. Upon dispersion in water, the π* transitions from sp2-hybridized carbon disappear, and holes in the valence band are observed. Electronic supplementary information (ESI) available: Experimental methods, details on XAS/XES normalization and background correction procedures. See DOI: 10.1039/c4nr06639a

  17. Effects of polarization of polar semiconductor on electrical properties of poly(vinylidene fluoride-trifluoroethylene)/ZnO heterostructures

    International Nuclear Information System (INIS)

    Yamada, Hiroaki; Yoshimura, Takeshi; Fujimura, Norifumi

    2015-01-01

    The electrical properties of heterostructures composed of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) and ZnO with different crystallographic polarities, i.e., O- and Zn-polar ZnO, were investigated. Distinct differences in the capacitance-voltage and polarization-voltage characteristics between the P(VDF-TrFE)/O- and Zn-polar ZnO were obtained in the depletion regions of ZnO. The band configurations were determined by X-ray photoelectron spectroscopy (XPS) using a synchrotron radiation beam to analyze the differences in the electrical properties of the P(VDF-TrFE)/O- and Zn-polar ZnO. The XPS spectra indicated that the valence band maximum of P(VDF-TrFE) is 2.9 and 2.7 eV higher than Zn- and O-polar ZnO, respectively. Thus, both structures have staggered band configurations with large valence band offsets, and the spontaneous polarization of ZnO is less effective on the band lineup. The electrical properties of the P(VDF-TrFE)/ZnO heterostructures are modulated through carrier generation because of the polarization-mediated interface charges and the staggered band alignments of the P(VDF-TrFE)/ZnO with a large valence band offset

  18. Band alignment measurements at heterojunction interfaces in layered thin film solar cells & thermoelectrics

    Science.gov (United States)

    Fang, Fang

    2011-12-01

    Public awareness of the increasing energy crisis and the related serious environmental concerns has led to a significantly growing demand for alternative clean and renewable energy resources. Thin film are widely applied in multiple renewable energy devices owing to the reduced amount of raw materials and increase flexibility of choosing from low-cost candidates, which translates directly into reduced capital cost. This is a key driving force to make renewable technology competitive in the energy market. This thesis is focused on the measurement of energy level alignments at interfaces of thin film structures for renewable energy applications. There are two primary foci: II -VI semiconductor ZnSe/ZnTe thin film solar cells and Bi2Te3/Sb2Te3 thin film structures for thermoelectric applications. In both cases, the electronic structure and energy band alignment at interfaces usually controls the carrier transport behavior and determines the quality of the device. High-resolution photoemission spectroscopy (lab-based XPS & synchrotron-based UPS) was used to investigate the chemical and electronic properties of epitaxial Bi2Te3 and Sb2Te3 thin films, in order to validate the anticipated band alignment at interfaces in Bi 2Te3/Sb2Te3 superlattices as one favoring electron-transmission. A simple, thorough two-step treatment of a chemical etching in dilute hydrochloric acid solution and a subsequent annealing at ˜150°C under ultra-high vacuum environment is established to remove the surface oxides completely. It is an essential step to ensure the measurements on electronic states are acquired on stoichimetric, oxide-free clean surface of Bi 2Te3 and Sb2Te3 films. The direct measurement of valence band offsets (VBO) at a real Sb 2Te3/Bi2Te3 interface is designed based on the Kraut model; a special stacking film structure is prepared intentionally: sufficiently thin Sb2Te3 film on top of Bi2Te 3 that photoelectrons from both of them are collected simultaneously. From a

  19. Intermixing, band alignment and charge transport in AgIn5S8/CuI heterojunctions

    International Nuclear Information System (INIS)

    Konovalov, I.; Makhova, L.; Hesse, R.; Szargan, R.

    2005-01-01

    Possibilities of creating photovoltaic devices using CuI/AgIn 5 S 8 heterojunctions are considered. Among other properties, preferential formation of polar (111) surfaces makes n-type AgIn 5 S 8 an attractive candidate for absorber layers of top cells in 4-terminal tandem structures. Cu-Ag exchange at the interface with p-type CuI was observed. This intermixing results in an additional component of Ag 3d5 photoelectron line after deposition of CuI, in the Cu (but not I) contamination of the surface after a chemical removal of CuI, and in a photoelectric sensitivity of the junction at energies below the band gaps. Valence band offsets of 0.4 and 0.5 eV (cliff) were found at interfaces with thin film and bulk AgIn 5 S 8 , supporting a conduction mechanism through interface recombination. Pinning conflict at the interface between materials with contradictory doping limitations is likely to promote the intermixing

  20. Thermal evolution of the band edges of 6H-SiC: X-ray methods compared to the optical band gap

    International Nuclear Information System (INIS)

    Miedema, P.S.; Beye, M.; Könnecke, R.; Schiwietz, G.; Föhlisch, A.

    2014-01-01

    Highlights: • Conduction band minima (CBM) of 6H-SiC are estimated with Si 2p XAS. • Valence band maxima (VBM) of 6H-SiC are estimated with non-resonant Si 2p XES. • Temperature-dependent VBM and CBM of 6H-SiC show asymmetric band gap closing. • XAS, XES and RIXS band gap estimates are compared with the optical band gap. • XAS + XES versus optical band gap provides core-excitonic screening energies. - Abstract: The band gap of semiconductors like silicon and silicon carbide (SiC) is the key for their device properties. In this research, the band gap of 6H-SiC and its temperature dependence were analyzed with silicon 2p X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS) allowing for a separate analysis of the conduction-band minimum (CBM) and valence-band maximum (VBM) components of the band gap. The temperature-dependent asymmetric band gap shrinking of 6H-SiC was determined with a valence-band slope of +2.45 × 10 −4 eV/K and a conduction-band slope of −1.334 × 10 −4 eV/K. The apparent asymmetry, e.g., that two thirds of the band-gap shrinking with increasing temperature is due to the VBM evolution in 6H-SiC, is similar to the asymmetry obtained for pure silicon before. The overall band gap temperature-dependence determined with XAS and non-resonant XES is compared to temperature-dependent optical studies. The core-excitonic binding energy appearing in the Si 2p XAS is extracted as the main difference. In addition, the energy loss of the onset of the first band in RIXS yields to values similar to the optical band gap over the tested temperature range

  1. Micro-Valences: Affective valence in neutral everyday objects

    Directory of Open Access Journals (Sweden)

    Sophie eLebrecht

    2012-04-01

    Full Text Available Affective valence influences both our cognition and our perception of the world. Indeed, the speed and quality with which we recognize objects in a visual scene can vary dramatically depending on its affective content. However, affective processing of visual objects has been typically studied using only stimuli with strong affective valences (e.g., guns or roses. Here we explore whether affective valence must be strong or obvious to exert an effect on our perception. We conclude that the majority of objects carry some affective valence (micro-valences and, thus, nominally neutral objects are not really neutral. Functionally, the perception of valence in everyday objects facilitates perceptually-driven choice behavior, decision-making, and affective responses.

  2. Hetero-gate-dielectric double gate junctionless transistor (HGJLT) with reduced band-to-band tunnelling effects in subthreshold regime

    International Nuclear Information System (INIS)

    Ghosh, Bahniman; Mondal, Partha; Akram, M. W.; Bal, Punyasloka; Salimath, Akshay Kumar

    2014-01-01

    We propose a hetero-gate-dielectric double gate junctionless transistor (HGJLT), taking high-k gate insulator at source side and low-k gate insulator at drain side, which reduces the effects of band-to-band tunnelling (BTBT) in the sub-threshold region. A junctionless transistor (JLT) is turned off by the depletion of carriers in the highly doped thin channel (device layer) which results in a significant band overlap between the valence band of the channel region and the conduction band of the drain region, due to off-state drain bias, that triggers electrons to tunnel from the valence band of the channel region to the conduction band of the drain region leaving behind holes in the channel. These effects of band-to-band tunnelling increase the sub-threshold leakage current, and the accumulation of holes in the channel forms a parasitic bipolar junction transistor (n–p–n BJT for channel JLT) in the lateral direction by the source (emitter), channel (base) and drain (collector) regions in JLT structure in off-state. The proposed HGJLT reduces the subthreshold leakage current and suppresses the parasitic BJT action in off-state by reducing the band-to-band tunnelling probability. (semiconductor devices)

  3. Strongly correlated impurity band superconductivity in diamond: X-ray spectroscopic evidence

    Directory of Open Access Journals (Sweden)

    G. Baskaran

    2006-01-01

    Full Text Available In a recent X-ray absorption study in boron doped diamond, Nakamura et al. have seen a well isolated narrow boron impurity band in non-superconducting samples and an additional narrow band at the chemical potential in a superconducting sample. We interpret the beautiful spectra as evidence for upper Hubbard band of a Mott insulating impurity band and an additional metallic 'mid-gap band' of a conducting 'self-doped' Mott insulator. This supports the basic framework of a recent theory of the present author of strongly correlated impurity band superconductivity (impurity band resonating valence bond, IBRVB theory in a template of a wide-gap insulator, with no direct involvement of valence band states.

  4. Deduction of the chemical state and the electronic structure of Nd{sub 2}Fe{sub 14}B compound from X-ray photoelectron spectroscopy core-level and valence-band spectra

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jing; Liang, Le [School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Zhang, Lanting, E-mail: lantingzh@sjtu.edu.cn, E-mail: lmsun@sjtu.edu.cn [School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Hirano Institute for Materials Innovation, Shanghai Jiao Tong University, Shanghai 200240 (China); Sun, Limin, E-mail: lantingzh@sjtu.edu.cn, E-mail: lmsun@sjtu.edu.cn [Instrumental Analysis Center, Shanghai Jiao Tong University, Shanghai 200240 (China); Hirano, Shinichi [Hirano Institute for Materials Innovation, Shanghai Jiao Tong University, Shanghai 200240 (China)

    2014-10-28

    Characterization of chemical state and electronic structure of the technologically important Nd{sub 2}Fe{sub 14}B compound is attractive for understanding the physical nature of its excellent magnetic properties. X-ray photoelectron spectroscopy (XPS) study of such rare-earth compound is important and also challenging due to the easy oxidation of surface and small photoelectron cross-sections of rare-earth 4f electrons and B 2p electrons, etc. Here, we reported an investigation based on XPS spectra of Nd{sub 2}Fe{sub 14}B compound as a function of Ar ion sputtering time. The chemical state of Fe and that of B in Nd{sub 2}Fe{sub 14}B compound can be clearly determined to be 0 and −3, respectively. The Nd in Nd{sub 2}Fe{sub 14}B compound is found to have the chemical state of close to +3 instead of +3 as compared with the Nd in Nd{sub 2}O{sub 3}. In addition, by comparing the valence-band spectrum of Nd{sub 2}Fe{sub 14}B compound to that of the pure Fe, the contributions from Nd, Fe, and B to the valence-band structure of Nd{sub 2}Fe{sub 14}B compound is made more clear. The B 2p states and B 2s states are identified to be at ∼11.2 eV and ∼24.6 eV, respectively, which is reported for the first time. The contribution from Nd 4f states can be identified both in XPS core-level spectrum and XPS valence-band spectrum. Although Nd 4f states partially hybridize with Fe 3d states, Nd 4f states are mainly localized in Nd{sub 2}Fe{sub 14}B compound.

  5. Temperature dependent empirical pseudopotential theory for self-assembled quantum dots.

    Science.gov (United States)

    Wang, Jianping; Gong, Ming; Guo, Guang-Can; He, Lixin

    2012-11-28

    We develop a temperature dependent empirical pseudopotential theory to study the electronic and optical properties of self-assembled quantum dots (QDs) at finite temperature. The theory takes the effects of both lattice expansion and lattice vibration into account. We apply the theory to InAs/GaAs QDs. For the unstrained InAs/GaAs heterostructure, the conduction band offset increases whereas the valence band offset decreases with increasing temperature, and there is a type-I to type-II transition at approximately 135 K. Yet, for InAs/GaAs QDs, the holes are still localized in the QDs even at room temperature, because the large lattice mismatch between InAs and GaAs greatly enhances the valence band offset. The single-particle energy levels in the QDs show a strong temperature dependence due to the change of confinement potentials. Because of the changes of the band offsets, the electron wavefunctions confined in QDs increase by about 1-5%, whereas the hole wavefunctions decrease by about 30-40% when the temperature increases from 0 to 300 K. The calculated recombination energies of excitons, biexcitons and charged excitons show red shifts with increasing temperature which are in excellent agreement with available experimental data.

  6. Energy band structure and electrical properties of Ga-oxide/GaN interface formed by remote oxygen plasma

    Science.gov (United States)

    Yamamoto, Taishi; Taoka, Noriyuki; Ohta, Akio; Truyen, Nguyen Xuan; Yamada, Hisashi; Takahashi, Tokio; Ikeda, Mitsuhisa; Makihara, Katsunori; Nakatsuka, Osamu; Shimizu, Mitsuaki; Miyazaki, Seiichi

    2018-06-01

    The energy band structure of a Ga-oxide/GaN structure formed by remote oxygen plasma exposure and the electrical interface properties of the GaN metal–oxide–semiconductor (MOS) capacitors with the SiO2/Ga-oxide/GaN structures with postdeposition annealing (PDA) at various temperatures have been investigated. Reflection high-energy electron diffraction and X-ray photoelectron spectroscopy clarified that the formed Ga-oxide layer is neither a single nor polycrystalline phase with high crystallinity. We found that the energy band offsets at the conduction band minimum and at the valence band maximum between the Ga-oxide layer and the GaN surface were 0.4 and 1.2 ± 0.2 eV, respectively. Furthermore, capacitance–voltage (C–V) characteristics revealed that the interface trap density (D it) is lower than the evaluation limit of Terman method without depending on the PDA temperatures, and that the SiO2/Ga-oxide stack can work as a protection layer to maintain the low D it, avoiding the significant decomposition of GaN at the high PDA temperature of 800 °C.

  7. Levels of valence

    Directory of Open Access Journals (Sweden)

    Vera eShuman

    2013-05-01

    Full Text Available The distinction between the positive and the negative is fundamental in our emotional life. In appraisal theories, in particular in the component process model of emotion (Scherer, 1984, 2010, qualitatively different types of valence are proposed based on appraisals of (unpleasantness, goal obstructiveness/conduciveness, low or high power, self- (incongruence, and moral badness/goodness. This multifaceted conceptualization of valence is highly compatible with the frequent observation of mixed feelings in real life. However, it seems to contradict the one-dimensional conceptualization of valence often encountered in psychological theories, and the notion of valence as a common currency used to explain choice behavior. Here, we propose a framework to integrate the seemingly disparate conceptualizations of multifaceted valence and one-dimensional valence by suggesting that valence should be conceived at different levels, micro and macro. Micro-valences correspond to qualitatively different types of evaluations, potentially resulting in mixed feelings, whereas one-dimensional macro-valence corresponds to an integrative common currency to compare alternatives for choices. We propose that conceptualizing levels of valence may focus research attention on the mechanisms that relate valence at one level (micro to valence at another level (macro, leading to new hypotheses and addressing various concerns that have been raised about the valence concept, such as the valence-emotion relation.

  8. Levels of Valence

    Science.gov (United States)

    Shuman, Vera; Sander, David; Scherer, Klaus R.

    2013-01-01

    The distinction between the positive and the negative is fundamental in our emotional life. In appraisal theories, in particular in the component process model of emotion (Scherer, 1984, 2010), qualitatively different types of valence are proposed based on appraisals of (un)pleasantness, goal obstructiveness/conduciveness, low or high power, self-(in)congruence, and moral badness/goodness. This multifaceted conceptualization of valence is highly compatible with the frequent observation of mixed feelings in real life. However, it seems to contradict the one-dimensional conceptualization of valence often encountered in psychological theories, and the notion of valence as a common currency used to explain choice behavior. Here, we propose a framework to integrate the seemingly disparate conceptualizations of multifaceted valence and one-dimensional valence by suggesting that valence should be conceived at different levels, micro and macro. Micro-valences correspond to qualitatively different types of evaluations, potentially resulting in mixed feelings, whereas one-dimensional macro-valence corresponds to an integrative “common currency” to compare alternatives for choices. We propose that conceptualizing levels of valence may focus research attention on the mechanisms that relate valence at one level (micro) to valence at another level (macro), leading to new hypotheses, and addressing various concerns that have been raised about the valence concept, such as the valence-emotion relation. PMID:23717292

  9. Adaptively loaded SP-offset-QAM OFDM for IM/DD communication systems.

    Science.gov (United States)

    Zhao, Jian; Chan, Chun-Kit

    2017-09-04

    In this paper, we propose adaptively loaded set-partitioned offset quadrature amplitude modulation (SP-offset-QAM) orthogonal frequency division multiplexing (OFDM) for low-cost intensity-modulation direct-detection (IM/DD) communication systems. We compare this scheme with multi-band carrier-less amplitude phase modulation (CAP) and conventional OFDM, and demonstrate >40 Gbit/s transmission over 50-km single-mode fiber. It is shown that the use of SP-QAM formats, together with the adaptive loading algorithm specifically designed to this group of formats, results in significant performance improvement for all these three schemes. SP-offset-QAM OFDM exhibits greatly reduced complexity compared to SP-QAM based multi-band CAP, via parallelized implementation and minimized memory length for spectral shaping. On the other hand, this scheme shows better performance than SP-QAM based conventional OFDM at both back-to-back and after transmission. We also characterize the proposed scheme in terms of enhanced tolerance to fiber intra-channel nonlinearity and the potential to increase the communication security. The studies show that adaptive SP-offset-QAM OFDM is a promising IM/DD solution for medium- and long-reach optical access networks and data center connections.

  10. Valence band photoemission studies of clean metals

    International Nuclear Information System (INIS)

    Wehner, P.S.

    1978-04-01

    The application of Angle-Resolved Photoelectron Spectroscopy (ARPES) to crystalline solids and the utilization of such studies to illuminate several questions concerning the detailed electronic structure of such materials, are discussed. Specifically, by construction of a Direct Transition (DT) model and the utilization of energy-dependent angle-resolved normal photoemission in the photon energy range 32 eV < or = hν < or = 200 eV, the bulk band structure of copper is experimentally mapped out along three different directions in the Brillouin Zone; GAMMA to K, GAMMA to L, and GAMMA to X. In addition, various effects which influence the obtainable resolution in vector k-space, namely, thermal disorder, momentum broadening, and band mixing, are discussed and are shown to place severe limitations on the applicability of the DT model. Finally, a model for Angle-Resolved X-ray Photoelectron Spectroscopy (ARXPS) based on the symmetry of the initial-state wavefunctions is presented and compared to experimental results obtained from copper single crystals

  11. Valence one-electron and shake-up ionization bands of fluorene, carbazole and dibenzofuran

    International Nuclear Information System (INIS)

    Reza Shojaei, S.H.; Morini, Filippo; Deleuze, Michael S.

    2013-01-01

    Highlights: • The photoelectron spectra of the title compounds are assigned in details. • Shake-up lines are found to severely contaminate both π- and σ-ionization bands. • σ-ionization onsets are subject to severe vibronic coupling complications. • We compare the results of OVGF, ADC(3) and TDDFT calculations. - Abstract: A comprehensive study of the He (I) ultra-violet photoelectron spectra of fluorene, carbazole and dibenzofuran is presented with the aid of one-particle Green’s Function calculations employing the outer-valence Green’s Function (OVGF) approach and the third-order algebraic diagrammatic construction [ADC(3)] scheme, along with Dunning’s correlation consistent basis sets of double and triple zeta quality (cc-pVDZ, cc-pVTZ). Extrapolations of the ADC(3) results for the outermost one-electron π-ionization energies to the cc-pVTZ basis set enable theoretical insights into He (I) measurements within ∼0.15 eV accuracy, up to the σ-ionization onset. The lower ionization energy of carbazole is the combined result of mesomeric and electronic relaxation effects. OVGF/cc-pVDZ or OVGF/cc-pVTZ pole strengths smaller than 0.85 systematically corroborate a breakdown of the orbital picture of ionization at the ADC(3) level. Comparison is made with calculations of the lowest doublet–doublet excitation energies of the radical cation of fluorene, by means of time-dependent density functional theory (TDDFT)

  12. Interface energy band alignment at the all-transparent p-n heterojunction based on NiO and BaSnO3

    Science.gov (United States)

    Zhang, Jiaye; Han, Shaobo; Luo, Weihuang; Xiang, Shuhuai; Zou, Jianli; Oropeza, Freddy E.; Gu, Meng; Zhang, Kelvin H. L.

    2018-04-01

    Transparent oxide semiconductors hold great promise for many optoelectronic devices such as transparent electronics, UV-emitting devices, and photodetectors. A p-n heterojunction is the most ubiquitous building block to realize these devices. In this work, we report the fabrication and characterization of the interface properties of a transparent heterojunction consisting of p-type NiO and n-type perovskite BaSnO3. We show that high-quality NiO thin films can be epitaxially grown on BaSnO3 with sharp interfaces because of a small lattice mismatch (˜1.3%). The diode fabricated from this heterojunction exhibits rectifying behavior with a ratio of 500. X-ray photoelectron spectroscopy reveals a type II or "staggered" band alignment with valence and conduction band offsets of 1.44 eV and 1.86 eV, respectively. Moreover, a large upward band bending potential of 0.90 eV for BaSnO3 and a downward band bending potential of 0.15 eV for NiO were observed in the interface region. Such electronic properties have important implication for optoelectronic applications as the large built-in potential provides favorable energetics for photo-generated electron-hole separation/migration.

  13. Electronic structure investigation of MoS2 and MoSe2 using angle-resolved photoemission spectroscopy and ab initio band structure studies.

    Science.gov (United States)

    Mahatha, S K; Patel, K D; Menon, Krishnakumar S R

    2012-11-28

    Angle-resolved photoemission spectroscopy (ARPES) and ab initio band structure calculations have been used to study the detailed valence band structure of molybdenite, MoS(2) and MoSe(2). The experimental band structure obtained from ARPES has been found to be in good agreement with the theoretical calculations performed using the linear augmented plane wave (LAPW) method. In going from MoS(2) to MoSe(2), the dispersion of the valence bands decreases along both k(parallel) and k(perpendicular), revealing the increased two-dimensional character which is attributed to the increasing interlayer distance or c/a ratio in these compounds. The width of the valence band and the band gap are also found to decrease, whereas the valence band maxima shift towards the higher binding energy from MoS(2) to MoSe(2).

  14. Chemical states and electronic structure of a HfO(-2)/Ge(001) interface

    International Nuclear Information System (INIS)

    Seo, Kang-ill; McIntyre, Paul C.; Stanford U., Materials Sci. Dept.; Sun, Shiyu; Lee, Dong-Ick; Pianetta, Piero; SLAC, SSRL; Saraswat, Krishna C.; Stanford U., Elect. Eng. Dept.

    2005-01-01

    We report the chemical bonding structure and valence band alignment at the HfO 2 /Ge (001) interface by systematically probing various core level spectra as well as valence band spectra using soft x-rays at the Stanford Synchrotron Radiation Laboratory. We investigated the chemical bonding changes as a function of depth through the dielectric stack by taking a series of synchrotron photoemission spectra as we etched through the HfO 2 film using a dilute HF-solution. We found that a very non-stoichiometric GeO x layer exists at the HfO 2 /Ge interface. The valence band spectra near the Fermi level in each different film structure were carefully analyzed, and as a result, the valence band offset between Ge and GeO x was determined to be ΔE v (Ge-GeO x ) = 2.2 ± 0.15 eV, and that between Ge and HfO 2 , ΔE v (Ge-HfO 2 ) = 2.7 ± 0.15 eV

  15. Valence band electronic structure of Ho-doped La0.67Ca0.33MnO3 using ultra-violet photoemission spectroscopy

    Science.gov (United States)

    Rout, S. K.; Mukharjee, R. N.; Mishra, D. K.; Roul, B. K.; Sekhar, B. R.; Dalai, M. K.

    2017-05-01

    In this manuscript we report the valence band electronic structure of Ho doped La0.67Ca0.33MnO3 using ultraviolet photoemission spectroscopy. We compared the density of states of La0.67Ca0.33MnO3, La0.67Ca0.3Ho0.03MnO3 and La0.64Ho0.03Ca0.33MnO3 near the Fermi level at various temperatures. Significant amount of changes have been observed at higher temperatures (220 K and 300 K) where the near Fermi level density of states increases with Ho doping into La0.67Ca0.33MnO3 indicating the enhancement of magnitude of change in metallicity (conductivity).

  16. Band structure of Si/Ge core-shell nanowires along the [110] direction modulated by external uniaxial strain

    International Nuclear Information System (INIS)

    Peng Xihong; Tang Fu; Logan, Paul

    2011-01-01

    Strain modulated electronic properties of Si/Ge core-shell nanowires along the [110] direction were reported, on the basis of first principles density-functional theory calculations. In particular, the energy dispersion relationship of the conduction/valence band was explored in detail. At the Γ point, the energy levels of both bands are significantly altered by applied uniaxial strain, which results in an evident change of the band gap. In contrast, for the K vectors far away from Γ, the variation of the conduction/valence band with strain is much reduced. In addition, with a sufficient tensile strain (∼1%), the valence band edge shifts away from Γ, which indicates that the band gap of the Si/Ge core-shell nanowires experiences a transition from direct to indirect. Our studies further showed that effective masses of charge carriers can also be tuned using the external uniaxial strain. The effective mass of the hole increases dramatically with tensile strain, while strain shows a minimal effect on tuning the effective mass of the electron. Finally, the relation between strain and the conduction/valence band edge is discussed thoroughly in terms of site-projected wavefunction characters.

  17. Black-body anomaly: analysis of temperature offsets

    International Nuclear Information System (INIS)

    Szopa, M.; Hofmann, R.; Schwarz, M.; Giacosa, F.

    2008-01-01

    Based on the postulate that photon propagation is governed by a dynamically broken SU(2) gauge symmetry (scale ∝10 -4 eV) we make predictions for temperature offsets due to a low-temperature (a few times the present CMB temperature) spectral anomaly at low frequencies. Temperature offsets are extracted from least-square fits of the anomalous black-body spectra to their conventional counterparts. We discuss statistical errors, compare our results with those obtained from calibration data of the FIRAS instrument, and point out that our predicted offsets are screened by experimental errors given the frequency range used by FIRAS to perform their spectral fits. We also make contact with the WMAP observation by blueshifting their frequency bands. Although our results hint towards a strong dynamical component in the CMB dipole and an explanation of low-l suppression, it is important in view of its particle-physics implications that the above postulate be verified/falsified by an independent low-temperature black-body precision experiment. (orig.)

  18. Micro-Valences: Affective valence in neutral everyday objects

    OpenAIRE

    Sophie eLebrecht; Moshe eBar; Lisa F Barrett; Michael J Tarr

    2012-01-01

    Affective valence influences both our cognition and our perception of the world. Indeed, the speed and quality with which we recognize objects in a visual scene can vary dramatically depending on its affective content. However, affective processing of visual objects has been typically studied using only stimuli with strong affective valences (e.g., guns or roses). Here we explore whether affective valence must be strong or obvious to exert an effect on our perception. We conclude that the maj...

  19. Automatic WEMVA by Focusing Subsurface Offset Virtual Sources

    KAUST Repository

    Sun, Bingbing

    2017-05-26

    Macro velocity building is important for subsequent prestack depth migration and full waveform inversion. Wave equation migration velocity analysis (WEMVA) utilizes band-limited waveform to invert the velocity in an automatic manner. Normally, inversion would be implemented by focusing the subsurface offset common image gathers(SOCIGs). We re-examine it with a different perspective and propose to view the SOCIGs and the background wavefield together as subsurface offset virtual sources(SOVS). A linear system connecting the perturbation of the position of those SOVS and velocity is derived and solved subsequently using a conjugate gradient method. Both synthetic and real dataset examples verify the correctness and effectiveness of the proposed method.

  20. Structure and method for controlling band offset and alignment at a crystalline oxide-on-semiconductor interface

    Science.gov (United States)

    McKee, Rodney A.; Walker, Frederick J.

    2003-11-25

    A crystalline oxide-on-semiconductor structure and a process for constructing the structure involves a substrate of silicon, germanium or a silicon-germanium alloy and an epitaxial thin film overlying the surface of the substrate wherein the thin film consists of a first epitaxial stratum of single atomic plane layers of an alkaline earth oxide designated generally as (AO).sub.n and a second stratum of single unit cell layers of an oxide material designated as (A'BO.sub.3).sub.m so that the multilayer film arranged upon the substrate surface is designated (AO).sub.n (A'BO.sub.3).sub.m wherein n is an integer repeat of single atomic plane layers of the alkaline earth oxide AO and m is an integer repeat of single unit cell layers of the A'BO.sub.3 oxide material. Within the multilayer film, the values of n and m have been selected to provide the structure with a desired electrical structure at the substrate/thin film interface that can be optimized to control band offset and alignment.

  1. Policy development for biodiversity offsets: a review of offset frameworks.

    Science.gov (United States)

    McKenney, Bruce A; Kiesecker, Joseph M

    2010-01-01

    Biodiversity offsets seek to compensate for residual environmental impacts of planned developments after appropriate steps have been taken to avoid, minimize or restore impacts on site. Offsets are emerging as an increasingly employed mechanism for achieving net environmental benefits, with offset policies being advanced in a wide range of countries (i.e., United States, Australia, Brazil, Colombia, and South Africa). To support policy development for biodiversity offsets, we review a set of major offset policy frameworks-US wetlands mitigation, US conservation banking, EU Natura 2000, Australian offset policies in New South Wales, Victoria, and Western Australia, and Brazilian industrial and forest offsets. We compare how the frameworks define offset policy goals, approach the mitigation process, and address six key issues for implementing offsets: (1) equivalence of project impacts with offset gains; (2) location of the offset relative to the impact site; (3) "additionality" (a new contribution to conservation) and acceptable types of offsets; (4) timing of project impacts versus offset benefits; (5) offset duration and compliance; and (6) "currency" and mitigation replacement ratios. We find substantial policy commonalities that may serve as a sound basis for future development of biodiversity offsets policy. We also identify issues requiring further policy guidance, including how best to: (1) ensure conformance with the mitigation hierarchy; (2) identify the most environmentally preferable offsets within a landscape context; and (3) determine appropriate mitigation replacement ratios.

  2. The observation of valence band change on resistive switching of epitaxial Pr{sub 0.7}Ca{sub 0.3}MnO{sub 3} film using removable liquid electrode

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Hong-Sub; Park, Hyung-Ho, E-mail: hhpark@yonsei.ac.kr [Department of Materials Science and Engineering, Yonsei University, Seodaemun-Ku, Seoul 120-749 (Korea, Republic of)

    2015-12-07

    The resistive switching (RS) phenomenon in transition metal oxides (TMOs) has received a great deal of attention for non-volatile memory applications. Various RS mechanisms have been suggested as to explain the observed RS characteristics. Many reports suggest that changes of interface and the role of oxygen vacancies originate in RS phenomena; therefore, in this study, we use a liquid drop of mercury as the top electrode (TE), epitaxial Pr{sub 0.7}Ca{sub 0.3}MnO{sub 3} (PCMO) (110) film of the perovskite manganite family for RS material, and an Nb-doped (0.7 at. %) SrTiO{sub 3} (100) single crystal as the substrate to observe changes in the interface between the TE and TMOs. The use of removable liquid electrode Hg drop as TE not only enables observation of the RS characteristic as a bipolar RS curve (counterclockwise) but also facilitates analysis of the valence band of the PCMO surface after resistive switching via photoelectron spectroscopy. The observed I-V behaviors of the low and high resistance states (HRS) are explained with an electrochemical migration model in PCMO film where accumulated oxygen vacancies at the interface between the Hg TE and PCMO (110) surface induce the HRS. The interpreted RS mechanism is directly confirmed via valence band spectrum analysis.

  3. Energy band alignment of antiferroelectric (Pb,La)(Zr,Sn,Ti)O{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Klein, Andreas, E-mail: aklein@surface.tu-darmstadt.de [Technische Universität Darmstadt, Institute of Materials Science, Surface Science Division, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); Lohaus, Christian [Technische Universität Darmstadt, Institute of Materials Science, Surface Science Division, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); Reiser, Patrick [Technische Universität Darmstadt, Institute of Materials Science, Surface Science Division, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); InnovationLab GmbH, Speyerer Straße 4, 69115 Heidelberg (Germany); Dimesso, Lucangelo [Technische Universität Darmstadt, Institute of Materials Science, Surface Science Division, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); Wang, Xiucai; Yang, Tongqing [Tongji University, Key Laboratory of Advanced Civil Engineering Materials (Ministry of Education), Functional Materials Research Laboratory, College of Materials Science and Engineering, Cao’an Road 4800, Shanghai 201804 (China)

    2017-06-15

    Highlights: • Energy band alignment of antiferroelectric PLZST studied by XPS. • A deconvolution procedure is applied to study band alignment of insulating materials. • Contribution of Pb 6s orbitals leads to higher valence band maximum. • Ferroelectric polarization does not contribute to valence band maximum energy. • The variation of Schottky barrier heights indicates no Fermi level pinning in PLZST. - Abstract: The energy band alignment of antiferroelectric (Pb,La)(Zr,Sn,Ti)O{sub 3} is studied with photoelectron spectroscopy using interfaces with high work function RuO{sub 2} and low work function Sn-doped In{sub 2}O{sub 3} (ITO). It is demonstrated how spectral deconvolution can be used to determine absolute Schottky barrier heights for insulating materials with a high accuracy. Using this approach it is found that the valence band maximum energy of (Pb,La)(Zr,Sn,Ti)O{sub 3} is found to be comparable to that of Pb- and Bi-containing ferroelectric materials, which is ∼1 eV higher than that of BaTiO{sub 3}. The results provide additional evidence for the occupation of the 6s orbitals as origin of the higher valence band maximum, which is directly related to the electrical properties of such compounds. The results also verify that the energy band alignment determined by photoelectron spectroscopy of as-deposited electrodes is not influenced by polarisation. The electronic structure of (Pb,La)(Zr,Sn,Ti)O{sub 3} should enable doping of the material without strongly modifying its insulating properties, which is crucial for high energy density capacitors. Moreover, the position of the energy bands should result in a great freedom of selecting electrode materials in terms of avoiding charge injection.

  4. Polarization Dependent Bulk-sensitive Valence Band Photoemission Spectroscopy and Density Functional Theory Calculations: Part I. 3d Transition Metals

    Science.gov (United States)

    Ueda, Shigenori; Hamada, Ikutaro

    2017-12-01

    The X-ray polarization dependent valence band HAXPES spectra of 3d transition metals (TMs) of Ti-Zn were measured to investigate the orbital resolved electronic structures by utilizing that the fact the photoionization cross-section of the atomic orbitals strongly depends on the experimental geometry. We have calculated the HAXPES spectra, which correspond to the cross-section weighted densities of states (CSW-DOSs), where the DOSs were obtained by the density functional theory calculations, and we have determined the relative photoionization cross-sections of the 4s and 4p orbitals to the 3d orbital in the 3d TMs. The experimentally obtained bulk-sensitive 3d and 4s DOSs were good agreement with the calculated DOSs in Ti, V, Cr, and Cu. In contrast, the deviations between the experimental and calculated 3d DOSs for Mn, Fe, Co, Ni were found, suggesting that the electron correlation plays an important role in the electronic structures for these materials.

  5. Relation between plasmons and the valence-band density-of-states in polymethylmethacrylate - influence of ion irradiation on damage selectivity

    International Nuclear Information System (INIS)

    Moliton, J.P.; Jussiaux, C.; Trigaud, T.; Lazzaroni, R.; Lhost, O.; Bredas, J.L.; Kihn, Y.; Sevely, J.

    1996-01-01

    A physical model is presented that aims at rationalizing the selectivity of bond breakage observed when polymethylmethacrylate is irradiated by ions in the 10-500 keV energy range. This model, previously proposed by Brandt and Ritchie, is based on electronic collective effects. The coupling between the pure plasma oscillation at omega(p) and the oscillation of free electrons at [omega(k0)(2)](1/2) makes the whole electronic population resonant at the frequency omega(rp) = (omega(p)(2) + [omega(k0)(2)])(1/2). By computing the valence-band density of states, we calculate [omega(k0)(2)] and then deduce the theoretical value of omega(rp). On the other hand, we provide an experimental measurement of omega(rp) and study its dependence on ion fluence by electron-energy-loss spectroscopy. The validity of the model of Brandt and Ritchie is then discussed in the light of both theoretical and experimental data. (author)

  6. Band structure of superlattice with δ-like potential

    International Nuclear Information System (INIS)

    Gashimzade, N.F.; Gashimzade, F.M.; Hajiev, A.T.

    1993-08-01

    Band structure of superlattice with δ-like potential has been calculated taking into account interaction of carriers of different kinds. Superlattices of semiconductors with degenerated valence band and zero-gap semiconductors have been considered. For the latter semimetal-semiconductor transition has been obtained. (author). 8 refs, 1 fig

  7. Interface band gap narrowing behind open circuit voltage losses in Cu2ZnSnS4 solar cells

    DEFF Research Database (Denmark)

    Crovetto, Andrea; Palsgaard, Mattias Lau Nøhr; Gunst, Tue

    2017-01-01

    We present evidence that bandgap narrowing at the heterointerface may be a major cause of the large open circuit voltage deficit of Cu2ZnSnS4/CdS solar cells. Bandgap narrowing is caused by surface states that extend the Cu2ZnSnS4valence band into the forbidden gap. Those surface states...... are consistently found in Cu2ZnSnS4, but not in Cu2ZnSnSe4, by first-principles calculations. They do not simply arise from defects at surfaces but are an intrinsic feature of Cu2ZnSnS4 surfaces. By including those states in a device model, the outcome of previously published temperature-dependent open circuit...... voltage measurements on Cu2ZnSnS4 solar cells can be reproduced quantitatively without necessarily assuming a cliff-like conduction band offset with the CdS buffer layer. Our first-principles calculations indicate that Zn-based alternative buffer layers are advantageous due to the ability of...

  8. Electrical properties and band structures of Pb1-x Snx Te alloys

    International Nuclear Information System (INIS)

    Ocio, Miguel

    1972-01-01

    Both p type alloys Pb 0.72 Sn 0.28 Te and Pb 0.53 Sn 0.47 Te have been studied in the present work. The main obtained results are the following: the materials have a two-valence band structure, the first band following non-parabolic Cohen's dispersion law; at low temperatures, carriers are scattered by ionized impurities; the Coulomb potentials being screened almost completely, impurities act like neutral centers. At room temperature, scattering by acoustic modes can explain lattice mobility behavior; reversing of the thermo-power, for samples with carrier densities of about 10 20 cm -3 , is possibly due to inter-band scattering between both valence bands; a very simple picture of the band parameters variations as a function of alloy fraction is suggested. (author) [fr

  9. Valence evaluation with approaching or withdrawing cues: directly testing valence-arousal conflict theory.

    Science.gov (United States)

    Wang, Yan Mei; Li, Ting; Li, Lin

    2017-07-19

    The valence-arousal conflict theory assumes that both valence and arousal will trigger approaching or withdrawing tendencies. It also predicts that the speed of processing emotional stimuli will depend on whether valence and arousal trigger conflicting or congruent motivational tendencies. However, most previous studies have provided evidence of the interaction between valence and arousal only, and have not provided direct proof of the interactive links between valence, arousal and motivational tendencies. The present study provides direct evidence for the relationship between approach-withdrawal tendencies and the valence-arousal conflict. In an empirical test, participants were instructed to judge the valence of emotional words after visual-spatial cues that appeared to be either approaching or withdrawing from participants. A three-way interaction (valence, arousal, and approach-withdrawal tendency) was observed such that the response time was shorter if participants responded to a negative high-arousal stimulus after a withdrawing cue, or to a positive low-arousal stimulus after an approaching cue. These findings suggest that the approach-withdrawal tendency indeed plays a crucial role in valence-arousal conflict, and that the effect depends on the congruency of valence, arousal and tendency at an early stage of processing.

  10. Band-offsets at BaTiO3/Cu2O heterojunction and enhanced photoelectrochemical response: theory and experiment(Conference Presentation)

    Science.gov (United States)

    Sharma, Dipika; Satsangi, Vibha R.; Dass Kaura, Sahab; Shrivastav, Rohit; Waghmare, Umesh V.

    2016-10-01

    Band-offsets at BaTiO3/Cu2O heterojunction and enhanced photoelectrochemical response: theory and experiment Dipika Sharmaa, Vibha R. Satsangib, Rohit Shrivastava, Umesh V. Waghmarec, Sahab Dassa aDepartment of Chemistry, Dayalbagh Educational Institute, Agra-282 110 (India) bDepartment of Physics and Computer Sciences, Dayalbagh Educational Institute, Agra-282 110 (India) cTheoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore-560 064 (India) * Phone: +91-9219695960. Fax: +91-562-2801226. E-mail: drsahabdas@gmail.com. Study on photoelectrochemical activity of pristine BaTiO3, Cu2O and BaTiO3/Cu2O heterojunction has been carried out using DFT based band offsets and charge carriers effective mass calculations and their experimental verification. The results of DFT calculations show that BaTiO3 and Cu2O have staggered type band alignment after the heterojunction formation and high mobility of electrons in Cu2O as compared to the electrons in BaTiO3. Staggered type band edges alignment and high mobility of electrons and holes improved the separation of photo-generated charge carriers in BaTiO3/Cu2O heterojunction. To validate the theoretical results experiments were carried out on pristine BaTiO3, Cu2O and BaTiO3/Cu2O heterojunction with varying thickness of Cu2O. All samples were characterized by X- Ray Diffractometer, SEM and UV-Vis spectrometry. Nanostructured thin films of pristine BaTiO3, Cu2O and BaTiO3/Cu2O heterojunction were used as photoelectrode in the photoelectrochemical cell for water splitting reaction. Maximum photocurrent density of 1.44 mA/cm2 at 0.90 V/SCE was exhibited by 442 nm thick BaTiO3/Cu2O heterojunction photoelectrode Increased photocurrent density and enhanced photoconversion efficiency, exhibited by the heterojunction may be attributed to improved conductivity and enhanced separation of the photogenerated carriers at the BaTiO3/Cu2O interface. The experimental results and first

  11. Semiconductor band alignment from first principles: a new nonequilibrium Green's function method applied to the CZTSe/CdS interface for photovoltaics

    DEFF Research Database (Denmark)

    Palsgaard, Mattias Lau Nøhr; Crovetto, Andrea; Gunst, Tue

    2016-01-01

    In this paper we present a method to obtain the band offset of semiconductor heterointerfaces from Density Functional Theory together with the nonequilibrium Green's function method. Band alignment and detailed properties of the interface between Cu2ZnSnSe4 and CdS are extracted directly from first...... principles simulations. The interface is important for photovoltaics applications where in particular the band offsets are important for efficiency. The band bending pose a problem for accurate atomistic simulations of band offsets due to its long range. Here we investigate two different methods for dealing...... with band bending directly. One involves doping the materials to induce a shorter screening length. The other method is to apply a voltage bias across the interface to correct for the band bending. The calculated band offsets agree well with previous experimental and theoretical studies and, interestingly...

  12. Madelung and Hubbard interactions in polaron band model of doped organic semiconductors

    Science.gov (United States)

    Png, Rui-Qi; Ang, Mervin C.Y.; Teo, Meng-How; Choo, Kim-Kian; Tang, Cindy Guanyu; Belaineh, Dagmawi; Chua, Lay-Lay; Ho, Peter K.H.

    2016-01-01

    The standard polaron band model of doped organic semiconductors predicts that density-of-states shift into the π–π* gap to give a partially filled polaron band that pins the Fermi level. This picture neglects both Madelung and Hubbard interactions. Here we show using ultrahigh workfunction hole-doped model triarylamine–fluorene copolymers that Hubbard interaction strongly splits the singly-occupied molecular orbital from its empty counterpart, while Madelung (Coulomb) interactions with counter-anions and other carriers markedly shift energies of the frontier orbitals. These interactions lower the singly-occupied molecular orbital band below the valence band edge and give rise to an empty low-lying counterpart band. The Fermi level, and hence workfunction, is determined by conjunction of the bottom edge of this empty band and the top edge of the valence band. Calculations are consistent with the observed Fermi-level downshift with counter-anion size and the observed dependence of workfunction on doping level in the strongly doped regime. PMID:27582355

  13. Change in crystalline structure and band alignment in atomic-layer-deposited HfO{sub 2} on InPusing an annealing treatment

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Yu-Seon; Kim, Dae-Kyoung; Cho, Mann-Ho [Institute of Physics and Applied Physics, Yonsei University, Seoul 120-749 (Korea, Republic of); Seo, Jung-Hye [Division of Materials Science, Korea Basic Science Institute, Daejeon 305-333 (Korea, Republic of); Shon, Hyun Kyong; Lee, Tae Geol [Korea Research Institute of Standards and Science, Daejeon 305-540 (Korea, Republic of); Cho, Young Dae; Kim, Sun-Wook; Ko, Dae-Hong [Department of Material Science and Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Kim, Hyoungsub [School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

    2013-08-15

    Changes in structural characteristics and band alignments of atomic-layer-deposited HfO{sub 2} films on InP (001) as a function of annealing temperature and film thickness were investigated using various analytical techniques. After an annealing at temperatures over 500 C, the HfO{sub 2} films were converted into a fully crystalline structure with a tetragonal phase with no detectable interfacial layer between the film and the InP substrate. In-P-O states, produced by interfacial reactions, were increased during the post deposition annealing (PDA) process and oxides were detected in the surface region of the HfO{sub 2} film, indicating that In and P atoms had out-diffused. The E{sub g} value of the as-grown HfO{sub 2} film was found to be 5.80 {+-} 0.1 eV. After the PDA treatment, the optical band gap and valence band offset values were significantly affected by the interfacial oxide states between the HfO{sub 2} film and InP substrate. Moreover, band bending in InP, due to negative space charges generated by an unstable P-rich interfacial state during atomic layer deposition process was decreased after the annealing treatment. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  14. A study of the valence shell electronic states of s-triazine by photoabsorption spectroscopy and ab initio calculations

    DEFF Research Database (Denmark)

    Holland, D.M.P.; Shaw, D.A.; Stener, Mauro

    2016-01-01

    absorption bands due to excitation from the 1e00 or 6e0 orbitals. The interpretation of the experimental spectrum has been guided by transition energies and oscillator strengths, for Rydberg and valence states, calculated with the time-dependent version of density functional theory and with the coupled...... cluster linear response approach. The theoretical studies indicate that Rydberg/Rydberg and Rydberg/valence mixing is important....

  15. Study of the Effect of Simulated Rain on the Offset Parabolic Antenna at Ku-Band with Different Elevation Angles

    Directory of Open Access Journals (Sweden)

    H. Mostafa

    2007-01-01

    Full Text Available Effect of rain on the receiver antenna is a major factor to degrade the system performance in a frequency above 10 GHz. This paper deals with the wet antenna attenuation at Ku-band with three different frequencies at different rain rates. During the Ku-band propagation experiment, it was discovered that rain water on the antenna caused a significant attenuation. It is necessary to estimate the losses caused by water on the antenna in order to separate these losses from the atmospheric propagation losses. The experiment was done at USM Engineering Campus to study the attenuation for these physical parameters. A Ku-band RF signal was generated by a signal generator and transmitted via horn antenna. The signal was received using a smooth offset antenna of 60 cm by 54 cm (Astro dish and measured using spectrum analyzer. In order to simulate a rain, pipes with bores of a same distance were implemented. Three cases were considered: in the first case one pipe was used to simulate low rain rate, the second case two pipes were used to simulate medium rain rate, and the third case three pipes were used to simulate heavy rain rate. In addition, the tap was used to control the flow of water in order to get more values of rain rate. The total attenuation of RF signals due to water layer on the feed and on the reflector feed was found to be 3.1 dB at worst case. On the other hand, the attenuation of RF signal due to the feed only was 2.83 dB, so the major attenuation occur was due to feed.

  16. Intermediate valence spectroscopy

    International Nuclear Information System (INIS)

    Gunnarsson, O.; Schoenhammer, K.

    1987-01-01

    Spectroscopic properties of intermediate valence compounds are studied using the Anderson model. Due to the large orbital and spin degeneracy N/sub f/ of the 4f-level, 1/N/sub f/ can be treated as a small parameter. This approach provides exact T = 0 results for the Anderson impurity model in the limit N/sub f/ → ∞, and by adding 1/N/sub f/ corrections some properties can be calculated accurately even for N/sub f/ = 1 or 2. In particular valence photoemission and resonance photoemission spectroscopies are studied. A comparison of theoretical and experimental spectra provides an estimate of the parameters in the model. Core level photoemission spectra provide estimates of the coupling between the f-level and the conduction states and of the f-level occupancy. With these parameters the model gives a fair description of other electron spectroscopies. For typical parameters the model predicts two structures in the f-spectrum, namely one structure at the f-level and one at the Fermi energy. The resonance photoemission calculation gives a photon energy dependence for these two peaks in fair agreement with experiment. The peak at the Fermi energy is partly due to a narrow Kondo resonance, resulting from many-body effects and the presence of a continuous, partly filled conduction band. This resonance is related to a large density of low-lying excitations, which explains the large susceptibility and specific heat observed for these systems at low temperatures. 38 references, 11 figures, 2 tables

  17. Noise-based frequency offset modulation in wideband frequency-selective fading channels

    NARCIS (Netherlands)

    Meijerink, Arjan; Cotton, S.L.; Bentum, Marinus Jan; Scanlon, W.G.

    2009-01-01

    A frequency offset modulation scheme using wideband noise carriers is considered. The main advantage of such a scheme is that it enables fast receiver synchronization without channel adaptation, while providing robustness to multipath fading and in-band interference. This is important for low-power

  18. Valencies of the lanthanides

    OpenAIRE

    Johnson, David A.; Nelson, Peter G.

    2018-01-01

    The valencies of the lanthanides vary more than was once thought. In addition to valencies associated with a half-full shell, there are valencies associated with a quarter- and three-quarter-full shell. This can be explained on the basis of Slater’s theory of many-electron atoms. The same theory explains the variation in complexing constants in the trivalent state (the “tetrad effect”). Valency in metallic and organometallic compounds is also discussed.

  19. Chemical state analysis of heat-treated 6, 13-bis(triisopropylsilylethynyl) pentacene investigated by XPS valence band spectra, XANES spectra and first-principles calculation

    International Nuclear Information System (INIS)

    Muro, Maiko; Natsume, Yutaka; Kikuma, Jun; Setoyama, Hiroyuki

    2014-01-01

    X-ray photoelectron spectroscopy (XPS) valence band spectra reflect the chemical bonding states. To take this advantage, we tried to interpret experimental spectra by the occupied density of states (DOS) based on first principles calculation. In this work, we discussed XPS and X-ray Absorption Near Edge Structure (XANES) spectra of 6, 13-bis(triisopropylsilylethynyl) pentacene (TIPS-Pen), which is well known as an organic semiconductor. We studied chemical structure change of TIPS-Pen caused by heat-treatment at 300degC under nitrogen and under the air. It has been suggested that the structural change of pentacene skeleton by Diels-Alder type reaction occurs in both cases. In addition, the sample heat-treated under the air showed desorption of the isopropyl group and increase of oxygen concentration. (author)

  20. Valence effects of sorption: laboratory control of valence state

    International Nuclear Information System (INIS)

    Meyer, R.E.; Arnold, W.D.; Case, F.I.

    1984-01-01

    Estimation of the rates of migration of nuclides from nuclear waste repositories required knowledge of the interaction of these nuclides with the components of the geological formations in the path of the migration. These interactions will be dependent upon the valence state and speciation of the nuclide. If the valence state is not known, then there can be little confidence in use of the data for safety analysis. An electrochemical method of valence state control was developed which makes use of a porous electrode in a flow system containing a column of the adsorbent. By use of this method and solvent extraction analyses of the valence states, a number of reactions of interest to HLW repositories were investigated. These include the reduction of Np(V) and Tc(VII) by crushed basalt and other minerals. For the reduction of Np(V) by basalt, the experiments indicate that sorption on basalt increases with pH and that most of the Np is reduced to Np(IV). The adsorbed Np(IV) is very difficult to remove from the basalt. For the experiments with Tc(VII), the results are considerably more complicated. The results of these experiments are used to assess some of the techniques and methods currently used in safety analyses of proposed HLW repositories. Perhaps the most important consideration is that predictive modeling of valence change reactions, such as the reduction of Np(V) and Tc(VII), must be used with considerable caution, and the occurrence of such reactions should be verified as best as possible with experiments using valence state control and analyses. 13 references, 3 figures, 1 table

  1. Observation of the c-f hybridization effect in valence-transition system EuPtP

    Energy Technology Data Exchange (ETDEWEB)

    Anzai, Hiroaki; Ichiki, Katsuya [Graduate School of Engineering, Osaka Prefecture University, Sakai (Japan); Schwier, Eike F.; Iwasawa, Hideaki; Arita, Masashi; Sato, Hitoshi; Shimada, Kenya; Namatame, Hirofumi; Taniguchi, Masaki [Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima (Japan); Mitsuda, Akihiro; Wada, Hirofumi [Graduate School of Science, Kyushu University, Fukuoka (Japan); Mimura, Kojiro [Graduate School of Engineering, Osaka Prefecture University, Sakai (Japan); Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima (Japan)

    2017-06-15

    We study the electronic structure of EuPtP, which exhibits two first-order valence transitions at T{sub 1} = 247 K and T{sub 2} = 201 K, using angle-resolved photoemission spectroscopy. Below T{sub 2}, we observe an energy gap at the crossing point of the bulk Eu 4f and conduction bands. The shape of band dispersions is described by a hybridization-band picture based on the periodic Anderson model. Our results demonstrate the c-f hybridization effect in the low-temperature phase of EuPtP. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  2. Band alignment studies of Al2O3/CuGaO2 and ZnO/CuGaO2 hetero-structures grown by pulsed laser deposition

    International Nuclear Information System (INIS)

    Ajimsha, R.S.; Das, Amit K.; Joshi, M.P.; Kukreja, L.M.

    2014-01-01

    Highlights: • Band offset studies at the interface of Al 2 O 3 /CuGaO 2 and ZnO/CuGaO 2 hetero-structures were performed using X-ray photoelectron spectroscopy. • Valance band offsets (VBO) of these hetero-structures were obtained from respective XPS peak positions and VB spectra using Kraut's equation. • Al 2 O 3 /CuGaO 2 interface exhibited a type I band alignment with valance band offset (VBO) of 4.05 eV whereas type II band alignment was observed in ZnO/CuGaO 2 hetero-structure with a VBO of 2.32 eV. • Schematic band alignment diagram for the interface of these hetero-structures has been constructed. • Band offset and alignment studies of these heterojunctions are important for gaining insight to the design of various optoelectronic devices based on such hetero-structures. - Abstract: We have studied the band offset and alignment of pulsed laser deposited Al 2 O 3 /CuGaO 2 and ZnO/CuGaO 2 hetero-structures using photoelectron spectroscopy. Al 2 O 3 /CuGaO 2 interface exhibited a type I band alignment with valance band offset (VBO) of 4.05 eV whereas type II band alignment was observed in ZnO/CuGaO 2 hetero-structure with a VBO of 2.32 eV. Schematic band alignment diagram for the interface of these hetero-structures has been constructed. Band offset and alignment studies of these heterojunctions are important for gaining insight to the design of various optoelectronic devices based on such hetero-structures

  3. Photoionization cross-sections of ground and excited valence levels of actinides

    Directory of Open Access Journals (Sweden)

    Yarzhemsky Victor G.

    2012-01-01

    Full Text Available The photoionization cross-sections of ground and excited atomic states of actinide atoms were calculated by the Dirac-Fock-Slater method for two excitation energies of X-ray radiation (1253.6 eV and 1486.6 eV. These data are required for calculations of intensities of X-ray photoelectron spectra of actinide compound valence bands and interpretation of experimental spectra.

  4. Pramana – Journal of Physics | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    The band alignment properties of the ZnTe/CrTe(0 0 1), CdTe/CrTe(0 0 1) and CdSe/CrTe(0 0 1) interfaces were computed and a rather large minority valence band offset of about 1.09 eV was observed in ZnTe/CrTe(0 0 1) heterojunction. Also in the CdTe/CrTe(0 0 1) and CdSe/CrTe(0 0 1) interfaces, the conduction band ...

  5. Effect of phase formation on valence band photoemission and photoresonance study of Ti/Ni multilayers using synchrotron radiation

    International Nuclear Information System (INIS)

    Bhatt, Pramod; Chaudhari, S.M.

    2006-01-01

    This paper presents investigation of Ti-Ni alloy phase formation and its effect on valence band (VB) photoemission and photoresonance study of as-deposited as well as annealed Ti/Ni multilayers (MLs) up to 600 deg. C using synchrotron radiation. For this purpose [Ti (50 A)/Ni (50 A)]X 10 ML structures were deposited by using electron-beam evaporation technique under ultra-high vacuum (UHV) conditions. Formation of different phases of Ti-Ni alloy due to annealing treatment has been confirmed by the X-ray diffraction (XRD) technique. The XRD pattern corresponding as-deposited ML sample shows crystalline nature of both Ti and Ni deposited layers, whereas 300 deg. C annealed ML sample show solid-state reaction (SSR) leading to amorphization and subsequent recrystallisation at higher temperatures of annealing (≥400 deg. C) with the formation of TiNi, TiNi 3 and Ti 2 Ni alloy phases. The survey scans corresponding to 400, 500 and 600 deg. C annealed ML sample shows interdiffusion and intermixing of Ni atoms into Ti layers leading to chemical Ti-Ni alloys phase formation at interface. The corresponding recorded VB spectra using synchrotron radiation at 134 eV on as-deposited ML sample with successive sputtering shows alternately photoemission bands due to Ti 3d and Ni 3d, respectively, indicating there is no mixing of the consequent layers and any phase formation at the interface during deposition. However, ML samples annealed at higher temperatures of annealing, particularly at 400, 500 and 600 deg. C show a clear shift in Ni 3d band and its satellite peak position to higher BE side indicates Ti-Ni alloy phase formation. In addition to this, reduction of satellite peak intensity and Ni 3d density of states (DOS) near Fermi level is also observed due to Ti-Ni phase formation with higher annealing temperatures. The variable photon energy VB measurements on as-deposited and ML samples annealed at 400 deg. C confirms existence and BE position of observed Ni 3d satellite

  6. Electronic band structure of lithium, sodium and potassium fluorides

    International Nuclear Information System (INIS)

    Jouanin, C.; Albert, J.P.; Gout, C.

    1975-01-01

    A mixed tight-binding, pseudopotential method is proposed to calculate the energy band structure of large-gap crystals and is tested here on LiF, NaF and KF. Three-centre terms are included in the determination of the valence bands by the tight-binding method and for the conduction bands we use a pseudopotential model proposed by Bassani and Giuliano, modified for the positive ions. By taking into account the polarization corrections, transitions calculated from the energy band structures are compared with experimental data and the agreement is generally good

  7. Type-I band alignment at MoS2/In0.15Al0.85N lattice matched heterojunction and realization of MoS2 quantum well

    KAUST Repository

    Tangi, Malleswarara

    2017-08-31

    The valence and conduction band offsets (VBO and CBO) at the semiconductor heterojunction are crucial parameters to design the active region of contemporary electronic and optoelectronic devices. In this report, to study the band alignment parameters at the In0.15Al0.85N/MoS2 lattice matched heterointerface, large area MoS2 single layers are chemical vapor deposited on molecular beam epitaxial grown In0.15Al0.85N films and vice versa. We grew InAlN having an in-plane lattice parameter closely matching with that of MoS2. We confirm that the grown MoS2 is a single layer from optical and structural analyses using micro-Raman spectroscopy and scanning transmission electron microscopy. The band offset parameters VBO and CBO at the In0.15Al0.85N/MoS2 heterojunction are determined to be 2.08 ± 0.15 and 0.60 ± 0.15 eV, respectively, with type-I band alignment using high-resolution x-ray photoelectron spectroscopy in conjunction with ultraviolet photoelectron spectroscopy. Furthermore, we design a MoS2 quantum well structure by growing an In0.15Al0.85N layer on MoS2/In0.15Al0.85N type-I heterostructure. By reducing the nitrogen plasma power and flow rate for the overgrown In0.15Al0.85N layers, we achieve unaltered structural properties and a reasonable preservation of photoluminescence intensity with a peak width of 70 meV for MoS2 quantum well (QW). The investigation provides a pathway towards realizing large area, air-stable, lattice matched, and eventual high efficiency In0.15Al0.85N/MoS2/In0.15Al0.85N QW-based light emitting devices.

  8. Orientation dependent band alignment for p-NiO/n-ZnO heterojunctions

    International Nuclear Information System (INIS)

    Ma, M. J.; Lu, B.; Zhou, T. T.; Ye, Z. Z.; Lu, J. G.; Pan, X. H.

    2013-01-01

    Nonpolor a-plane and polar c-plane ZnO thin films were prepared on r-plane sapphire and quartz substrates, respectively. The electronic structure of the interface between subsequently fabricated NiO/ZnO heterojunctions has been investigated by x-ray photoelectron spectroscopy measurements and the band offsets are determined together with information yielded from UV-vis transition spectra. It is found that a type-II band alignment forms at the interface for both the samples. The revealed ZnO-orientation dependent band offsets are analyzed and are attributed mainly due to the variations in internal electric field arose from spontaneous polarization effect. The accurate determination of the band alignment is important for the design and application of NiO/ZnO based hybrid devices.

  9. Orientation dependent band alignment for p-NiO/n-ZnO heterojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Ma, M. J.; Lu, B.; Zhou, T. T.; Ye, Z. Z.; Lu, J. G.; Pan, X. H. [State Key Laboratory of Silicon Materials, Cyrus Tang Center for Sensor Materials and Applications, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China)

    2013-04-28

    Nonpolor a-plane and polar c-plane ZnO thin films were prepared on r-plane sapphire and quartz substrates, respectively. The electronic structure of the interface between subsequently fabricated NiO/ZnO heterojunctions has been investigated by x-ray photoelectron spectroscopy measurements and the band offsets are determined together with information yielded from UV-vis transition spectra. It is found that a type-II band alignment forms at the interface for both the samples. The revealed ZnO-orientation dependent band offsets are analyzed and are attributed mainly due to the variations in internal electric field arose from spontaneous polarization effect. The accurate determination of the band alignment is important for the design and application of NiO/ZnO based hybrid devices.

  10. Band Structure Analysis of La0.7Sr0.3MnO3 Perovskite Manganite Using a Synchrotron

    Directory of Open Access Journals (Sweden)

    Hong-Sub Lee

    2015-01-01

    Full Text Available Oxide semiconductors and their application in next-generation devices have received a great deal of attention due to their various optical, electric, and magnetic properties. For various applications, an understanding of these properties and their mechanisms is also very important. Various characteristics of these oxides originate from the band structure. In this study, we introduce a band structure analysis technique using a soft X-ray energy source to study a La0.7Sr0.3MnO3 (LSMO oxide semiconductor. The band structure is formed by a valence band, conduction band, band gap, work function, and electron affinity. These can be determined from secondary electron cut-off, valence band spectrum, O 1s core electron, and O K-edge measurements using synchrotron radiation. A detailed analysis of the band structure of the LSMO perovskite manganite oxide semiconductor thin film was established using these techniques.

  11. Valence and conduction band offsets of β-Ga2O3/AlN heterojunction

    KAUST Repository

    Sun, Haiding; Torres Castanedo, C. G.; Liu, Kaikai; Li, Kuang-Hui; Guo, Wenzhe; Lin, Ronghui; Liu, Xinwei; Li, Jingtao; Li, Xiaohang

    2017-01-01

    Both β-Ga2O3 and wurtzite AlN have wide bandgaps of 4.5–4.9 and 6.1 eV, respectively. We calculated the in-plane lattice mismatch between the (−201) plane of β-Ga2O3 and the (0002) plane of AlN, which was found to be 2.4%. This is the smallest

  12. Change in optimum genetic algorithm solution with changing band discontinuities and band widths of electrically conducting copolymers

    Science.gov (United States)

    Kaur, Avneet; Bakhshi, A. K.

    2010-04-01

    The interest in copolymers stems from the fact that they present interesting electronic and optical properties leading to a variety of technological applications. In order to get a suitable copolymer for a specific application, genetic algorithm (GA) along with negative factor counting (NFC) method has recently been used. In this paper, we study the effect of change in the ratio of conduction band discontinuity to valence band discontinuity (Δ Ec/Δ Ev) on the optimum solution obtained from GA for model binary copolymers. The effect of varying bandwidths on the optimum GA solution is also investigated. The obtained results show that the optimum solution changes with varying parameters like band discontinuity and band width of constituent homopolymers. As the ratio Δ Ec/Δ Ev increases, band gap of optimum solution decreases. With increasing band widths of constituent homopolymers, the optimum solution tends to be dependent on the component with higher band gap.

  13. Offset drilling obligations

    International Nuclear Information System (INIS)

    Boyd, K.D.; Kalmakoff, J.J.

    1998-01-01

    A review of the 'offset well' clause found in freehold and Crown natural gas and petroleum leases was presented. The objective was to provide lessors and lessees with a clear understanding of the rights and obligations associated with offset wells. It was noted that offset well obligations vary according to the form of lease used, the type of offsetting well, the regulatory regime and the geophysical characteristics of the producing formation. Some suggestions were made as to how current versions of the offset well clause can be amended to overcome some of the problems encountered in applying the clause to an offset horizontal well that has been drilled on adjoining lands. Failure to resolve the new issues presented by horizontal drilling technology in terms of documentation, which records respective rights and obligations on the basis of generally accepted principles, will result in large numbers of conflicts and unnecessary litigation. 144 refs., 1 fig

  14. Computational Design of Flat-Band Material

    Science.gov (United States)

    Hase, I.; Yanagisawa, T.; Kawashima, K.

    2018-02-01

    Quantum mechanics states that hopping integral between local orbitals makes the energy band dispersive. However, in some special cases, there are bands with no dispersion due to quantum interference. These bands are called as flat band. Many models having flat band have been proposed, and many interesting physical properties are predicted. However, no real compound having flat band has been found yet despite the 25 years of vigorous researches. We have found that some pyrochlore oxides have quasi-flat band just below the Fermi level by first principles calculation. Moreover, their valence bands are well described by a tight-binding model of pyrochlore lattice with isotropic nearest neighbor hopping integral. This model belongs to a class of Mielke model, whose ground state is known to be ferromagnetic with appropriate carrier doping and on-site repulsive Coulomb interaction. We have also performed a spin-polarized band calculation for the hole-doped system from first principles and found that the ground state is ferromagnetic for some doping region. Interestingly, these compounds do not include magnetic element, such as transition metal and rare-earth elements.

  15. Determination of the band alignment of a-IGZO/a-IGMO heterojunction for high-electron mobility transistor application

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yi-Yu; Qian, Ling-Xuan; Liu, Xing-Zhao [School of Microelectronics and Solid-State Electronics, University of Electronic Science and Technology of China, Chengdu (China); State Key Laboratory of Electronic Thin Films and Integrated Devices, Chengdu (China)

    2017-10-15

    In the past decade, amorphous InGaZnO thin film transistors (a-IGZO TFTs) have become a very promising candidate for application in flat panel displays (FPDs). However, it is difficult to break through the mobility bottleneck of a-IGZO TFTs to obtain mobilities higher than 100 cm{sup 2} V{sup -1} s{sup -1}, thus limiting their use in more advanced applications. Construction of a high-electron mobility transistor (HEMT) based on a heterojunction structure could provide a solution for this problem. In this work, the band alignment of a-IGZO and amorphous InGaMgO (a-IGMO) heterojunction has been investigated using X-ray photoelectron spectroscopy (XPS) and transmission spectra measurements. The valence band (ΔE{sub V}) and conduction band offsets (ΔE{sub C}) were determined as 0.09 and 0.83 eV, respectively. The ΔE{sub C} was large enough to construct a potential well that could favor the appearance of a two-dimensional electron gas (2DEG). Hence, the achievement of an HEMT based on a-IGZO/a-IGMO heterojunction can be expected. Moreover, band bending contributed greatly to such a large ΔE{sub C}, and thus to the formation of electrical confinement structure. Our findings suggest that a-IGZO/a-IGMO heterojunction is a potential candidate for constructing a HEMT and thus breaking through the mobility bottleneck of a-IGZO-based TFTs for the applications in next-generation electronic products. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  16. Determination of the band alignment of a-IGZO/a-IGMO heterojunction for high-electron mobility transistor application

    International Nuclear Information System (INIS)

    Zhang, Yi-Yu; Qian, Ling-Xuan; Liu, Xing-Zhao

    2017-01-01

    In the past decade, amorphous InGaZnO thin film transistors (a-IGZO TFTs) have become a very promising candidate for application in flat panel displays (FPDs). However, it is difficult to break through the mobility bottleneck of a-IGZO TFTs to obtain mobilities higher than 100 cm"2 V"-"1 s"-"1, thus limiting their use in more advanced applications. Construction of a high-electron mobility transistor (HEMT) based on a heterojunction structure could provide a solution for this problem. In this work, the band alignment of a-IGZO and amorphous InGaMgO (a-IGMO) heterojunction has been investigated using X-ray photoelectron spectroscopy (XPS) and transmission spectra measurements. The valence band (ΔE_V) and conduction band offsets (ΔE_C) were determined as 0.09 and 0.83 eV, respectively. The ΔE_C was large enough to construct a potential well that could favor the appearance of a two-dimensional electron gas (2DEG). Hence, the achievement of an HEMT based on a-IGZO/a-IGMO heterojunction can be expected. Moreover, band bending contributed greatly to such a large ΔE_C, and thus to the formation of electrical confinement structure. Our findings suggest that a-IGZO/a-IGMO heterojunction is a potential candidate for constructing a HEMT and thus breaking through the mobility bottleneck of a-IGZO-based TFTs for the applications in next-generation electronic products. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  17. The role of the core in degeneracy of chiral candidate band doubling

    International Nuclear Information System (INIS)

    Timar, J.; Sohler, D.; Vaman, C.; SUNY, Stony Brook, NY; Starosta, K.; Fossan, D.B.; Koike, T.; Tohoku Univ., Sendai; Lee, I.Y.; Macchiavelli, A.O.

    2005-01-01

    Complete text of publication follows. Nearly degenerate ΔI=1 rotational bands have been observed recently in several odd-odd nuclei in the A ∼ 130 and A ∼ 100 mass regions. The properties of these doublet bands have been found to agree with the scenario of spontaneous formation of chirality and disagree with other possible scenarios. However, the most recent results obtained from life-time experiments for some chiral candidate nuclei in the A ∼ 130 mass region seem to contradict the chiral interpretation of the doublet bands in these nuclei based on the observed differences in the absolute electromagnetic transition rates; the transition rates expected for chiral doublets are predicted to be very similar. Therefore it is interesting to search for new types of experimental data that may provide further possibilities to distinguish between alternative interpretations, and may uncover new properties of the mechanism that is responsible for the band doubling in these nuclei. Such a new type of experimental data was found by studying the chiral candidate bands in neighboring Rh nuclei. High-spin states of 103 Rh were studied using the 96 Zr( 11 B,4n) reaction at 40 MeV beam energy and chiral partner candidate bands have been found in it. As a result of this observation a special quartet of neighboring chiral candidate nuclei can be investigated for the first time. With this quartet identified a comparison between the behavior of the nearly degenerate doublet bands belonging to the same core but to different valence quasiparticle configurations, as well as belonging to different cores but to the same valence quasiparticle configuration, becomes possible. The comparison shows that the energy separation of these doublet band structures depends mainly on the core properties and only at less extent on the valence quasiparticle coupling. This observation sets up new criteria for the explanations of the band doublings, restricting the possible scenarios and providing

  18. Wavelet-based study of valence-arousal model of emotions on EEG signals with LabVIEW.

    Science.gov (United States)

    Guzel Aydin, Seda; Kaya, Turgay; Guler, Hasan

    2016-06-01

    This paper illustrates the wavelet-based feature extraction for emotion assessment using electroencephalogram (EEG) signal through graphical coding design. Two-dimensional (valence-arousal) emotion model was studied. Different emotions (happy, joy, melancholy, and disgust) were studied for assessment. These emotions were stimulated by video clips. EEG signals obtained from four subjects were decomposed into five frequency bands (gamma, beta, alpha, theta, and delta) using "db5" wavelet function. Relative features were calculated to obtain further information. Impact of the emotions according to valence value was observed to be optimal on power spectral density of gamma band. The main objective of this work is not only to investigate the influence of the emotions on different frequency bands but also to overcome the difficulties in the text-based program. This work offers an alternative approach for emotion evaluation through EEG processing. There are a number of methods for emotion recognition such as wavelet transform-based, Fourier transform-based, and Hilbert-Huang transform-based methods. However, the majority of these methods have been applied with the text-based programming languages. In this study, we proposed and implemented an experimental feature extraction with graphics-based language, which provides great convenience in bioelectrical signal processing.

  19. Experimental studies of narrow band effects in the actinides

    Energy Technology Data Exchange (ETDEWEB)

    Brodsky, M.B.

    1976-01-01

    In many actinide metallic systems the f-electrons exhibit band behavior. This is a consequence of direct f-f wave function overlap or hybridization of f-electrons with s-, p-, and d-electrons. The f-bands can be responsible for large electronic densities of states at the Fermi level which may lead to band magnetism of various types. Although the concept of valence instabilities must be approached cautiously especially in the light actinides, it would not be surprising to observe them in the future, especially in Am compounds.

  20. Experimental studies of narrow band effects in the actinides

    International Nuclear Information System (INIS)

    Brodsky, M.B.

    1976-01-01

    In many actinide metallic systems the f-electrons exhibit band behavior. This is a consequence of direct f-f wave function overlap or hybridization of f-electrons with s-, p-, and d-electrons. The f-bands can be responsible for large electronic densities of states at the Fermi level which may lead to band magnetism of various types. Although the concept of valence instabilities must be approached cautiously especially in the light actinides, it would not be surprising to observe them in the future, especially in Am compounds

  1. Energies of rare-earth ion states relative to host bands in optical materials from electron photoemission spectroscopy

    Science.gov (United States)

    Thiel, Charles Warren

    There are a vast number of applications for rare-earth-activated materials and much of today's cutting-edge optical technology and emerging innovations are enabled by their unique properties. In many of these applications, interactions between the rare-earth ion and the host material's electronic states can enhance or inhibit performance and provide mechanisms for manipulating the optical properties. Continued advances in these technologies require knowledge of the relative energies of rare-earth and crystal band states so that properties of available materials may be fully understood and new materials may be logically developed. Conventional and resonant electron photoemission techniques were used to measure 4f electron and valence band binding energies in important optical materials, including YAG, YAlO3, and LiYF4. The photoemission spectra were theoretically modeled and analyzed to accurately determine relative energies. By combining these energies with ultraviolet spectroscopy, binding energies of excited 4fN-15d and 4fN+1 states were determined. While the 4fN ground-state energies vary considerably between different trivalent ions and lie near or below the top of the valence band in optical materials, the lowest 4f N-15d states have similar energies and are near the bottom of the conduction band. As an example for YAG, the Tb3+ 4f N ground state is in the band gap at 0.7 eV above the valence band while the Lu3+ ground state is 4.7 eV below the valence band maximum; however, the lowest 4fN-15d states are 2.2 eV below the conduction band for both ions. We found that a simple model accurately describes the binding energies of the 4fN, 4fN-1 5d, and 4fN+1 states. The model's success across the entire rare-earth series indicates that measurements on two different ions in a host are sufficient to predict the energies of all rare-earth ions in that host. This information provides new insight into electron transfer transitions, luminescence quenching, and valence

  2. Features of the core-valence luminescence and electron energy band structure of A1-xCsxCaCl3 (A = K,Rb) crystals

    International Nuclear Information System (INIS)

    Chornodolskyy, Ya; Stryganyuk, G; Syrotyuk, S; Voloshinovskii, A; Rodnyi, P

    2007-01-01

    From luminescence spectroscopy of CsCaCl 3 , Rb 1-x Cs x CaCl 3 and K 1-x Cs x CaCl 3 crystals, we have found evidence for intrinsic and impurity core-valence luminescence due to the radiative recombination of valence electrons with the holes of intrinsic or impurity 5p Cs + core states. The structural similarity of core-valence luminescence spectra has been revealed for the A 1-x Cs x CaCl 3 (A = K,Rb) crystals investigated. The electron energy structure of the CsCaCl 3 crystal has been calculated using the pseudopotential approach taking into account the gradient corrections for the exchange-correlation energy. The calculated density of the electronic states of CsCaCl 3 has been compared with corresponding parameters obtained from the analysis of core-valence luminescence spectra

  3. Valency and type conversion in CuInSe2 with H2 plasma exposure: A photoemission investigation

    International Nuclear Information System (INIS)

    Nelson, A.J.; Frigo, S.P.; Rosenberg, R.

    1993-01-01

    The effect of H 2 plasma exposure on CuInSe 2 was studied by synchrotron radiation soft-x-ray photoemission spectroscopy. The low-power H 2 plasma was generated with a commercial electron cyclotron resonance plasma source using pure H 2 with the plasma exposure being performed at 200 degree C. In situ photoemission measurements were acquired after each plasma exposure in order to observe changes in the valence-band electronic structure as well as changes in the In 4d and Se 3d core lines. The results were correlated in order to relate changes in surface chemistry to the electronic structure. These measurements indicate that the H 2 plasma exposure type converts the CuInSe 2 surface to an n-type surface as well as converting the In +3 valency state to an In +1 valency state

  4. Band structure of TiO sub 2 -doped yttria-stabilized zirconia probed by soft-x-ray spectroscopy

    CERN Document Server

    Higuchi, T; Kobayashi, K; Yamaguchi, S; Fukushima, A; Shin, S

    2003-01-01

    The electronic structure of TiO sub 2 -doped yttria-stabilized zirconia (YSZ) has been studied by soft-X-ray emission spectroscopy (SXES) and X-ray absorption spectroscopy (XAS). The valence band is mainly composed of the O 2p state. The O 1s XAS spectrum exhibits the existence of the Ti 3d unoccupied state under the Zr 4d conduction band. The intensity of the Ti 3d unoccupied state increases with increasing TiO sub 2 concentration. The energy separation between the top of the valence band and the bottom of the Ti 3d unoccupied state is in accord with the energy gap, as expected from dc-polarization and total conductivity measurements. (author)

  5. Electronic transitions and band offsets in C60:SubPc and C60:MgPc on MoO3 studied by modulated surface photovoltage spectroscopy

    International Nuclear Information System (INIS)

    Fengler, S.; Dittrich, Th.; Rusu, M.

    2015-01-01

    Electronic transitions at interfaces between MoO 3 layers and organic layers of C 60 , SubPc, MgPc, and nano-composite layers of SubPc:C 60 and MgPc:C 60 have been studied by modulated surface photovoltage (SPV) spectroscopy. For all systems, time dependent and modulated SPV signals pointed to dissociation of excitons at the MoO 3 /organic layer interfaces with a separation of holes towards MoO 3 . The highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps (E HL ) of C 60 , SubPc, and MgPc and the effective E HL of SubPc:C 60 and MgPc:C 60 were measured. The offsets between the LUMO (ΔE L ) or HOMO (ΔE H ) bands were obtained with high precision and amounted to 0.33 or 0.73 eV for SubPc:C 60 , respectively, and to −0.33 or 0.67 eV for MgPc:C 60 , respectively. Exponential tails below E HL and most pronounced sub-bandgap transitions were characterized and ascribed to disorder and transitions from HOMO bands to unoccupied defect states

  6. Modeling direct band-to-band tunneling: From bulk to quantum-confined semiconductor devices

    Science.gov (United States)

    Carrillo-Nuñez, H.; Ziegler, A.; Luisier, M.; Schenk, A.

    2015-06-01

    A rigorous framework to study direct band-to-band tunneling (BTBT) in homo- and hetero-junction semiconductor nanodevices is introduced. An interaction Hamiltonian coupling conduction and valence bands (CVBs) is derived using a multiband envelope method. A general form of the BTBT probability is then obtained from the linear response to the "CVBs interaction" that drives the system out of equilibrium. Simple expressions in terms of the one-electron spectral function are developed to compute the BTBT current in two- and three-dimensional semiconductor structures. Additionally, a two-band envelope equation based on the Flietner model of imaginary dispersion is proposed for the same purpose. In order to characterize their accuracy and differences, both approaches are compared with full-band, atomistic quantum transport simulations of Ge, InAs, and InAs-Si Esaki diodes. As another numerical application, the BTBT current in InAs-Si nanowire tunnel field-effect transistors is computed. It is found that both approaches agree with high accuracy. The first one is considerably easier to conceive and could be implemented straightforwardly in existing quantum transport tools based on the effective mass approximation to account for BTBT in nanodevices.

  7. Modeling direct band-to-band tunneling: From bulk to quantum-confined semiconductor devices

    International Nuclear Information System (INIS)

    Carrillo-Nuñez, H.; Ziegler, A.; Luisier, M.; Schenk, A.

    2015-01-01

    A rigorous framework to study direct band-to-band tunneling (BTBT) in homo- and hetero-junction semiconductor nanodevices is introduced. An interaction Hamiltonian coupling conduction and valence bands (CVBs) is derived using a multiband envelope method. A general form of the BTBT probability is then obtained from the linear response to the “CVBs interaction” that drives the system out of equilibrium. Simple expressions in terms of the one-electron spectral function are developed to compute the BTBT current in two- and three-dimensional semiconductor structures. Additionally, a two-band envelope equation based on the Flietner model of imaginary dispersion is proposed for the same purpose. In order to characterize their accuracy and differences, both approaches are compared with full-band, atomistic quantum transport simulations of Ge, InAs, and InAs-Si Esaki diodes. As another numerical application, the BTBT current in InAs-Si nanowire tunnel field-effect transistors is computed. It is found that both approaches agree with high accuracy. The first one is considerably easier to conceive and could be implemented straightforwardly in existing quantum transport tools based on the effective mass approximation to account for BTBT in nanodevices

  8. Modeling direct band-to-band tunneling: From bulk to quantum-confined semiconductor devices

    Energy Technology Data Exchange (ETDEWEB)

    Carrillo-Nuñez, H.; Ziegler, A.; Luisier, M.; Schenk, A. [Integrated Systems Laboratory ETH Zürich, Gloriastrasse 35, 8092 Zürich (Switzerland)

    2015-06-21

    A rigorous framework to study direct band-to-band tunneling (BTBT) in homo- and hetero-junction semiconductor nanodevices is introduced. An interaction Hamiltonian coupling conduction and valence bands (CVBs) is derived using a multiband envelope method. A general form of the BTBT probability is then obtained from the linear response to the “CVBs interaction” that drives the system out of equilibrium. Simple expressions in terms of the one-electron spectral function are developed to compute the BTBT current in two- and three-dimensional semiconductor structures. Additionally, a two-band envelope equation based on the Flietner model of imaginary dispersion is proposed for the same purpose. In order to characterize their accuracy and differences, both approaches are compared with full-band, atomistic quantum transport simulations of Ge, InAs, and InAs-Si Esaki diodes. As another numerical application, the BTBT current in InAs-Si nanowire tunnel field-effect transistors is computed. It is found that both approaches agree with high accuracy. The first one is considerably easier to conceive and could be implemented straightforwardly in existing quantum transport tools based on the effective mass approximation to account for BTBT in nanodevices.

  9. Carbon offsetting: sustaining consumption?

    OpenAIRE

    Heather Lovell; Harriet Bulkeley; Diana Liverman

    2009-01-01

    In this paper we examine how theories of sustainable and ethical consumption help us to understand a new, rapidly expanding type of consumer product designed to mitigate climate change: carbon offsets. The voluntary carbon offset market grew by 200% between 2005 and 2006, and there are now over 150 retailers of voluntary carbon offsets worldwide. Our analysis concentrates on the production and consumption of carbon offsets, drawing on ideas from governmentality and political ecology about how...

  10. Conduction-band valley spin splitting in single-layer H-T l2O

    Science.gov (United States)

    Ma, Yandong; Kou, Liangzhi; Du, Aijun; Huang, Baibiao; Dai, Ying; Heine, Thomas

    2018-02-01

    Despite numerous studies, coupled spin and valley physics is currently limited to two-dimensional (2D) transition-metal dichalcogenides (TMDCs). Here, we predict an exceptional 2D valleytronic material associated with the spin-valley coupling phenomena beyond 2D TMDCs—single-layer (SL) H-T l2O . It displays large valley spin splitting (VSS), significantly larger than that of 2D TMDCs, and a finite band gap, which are both critically attractive for the integration of valleytronics and spintronics. More importantly, in sharp contrast to all the experimentally confirmed 2D valleytronic materials, where the strong valence-band VSS (0.15-0.46 eV) supports the spin-valley coupling, the VSS in SL H-T l2O is pronounced in its conduction band (0.61 eV), but negligibly small in its valence band (21 meV), thus opening a way for manipulating the coupled spin and valley physics. Moreover, SL H-T l2O possesses extremely high carrier mobility, as large as 9.8 ×103c m2V-1s-1 .

  11. Size and alloying induced shift in core and valence bands of Pd-Ag and Pd-Cu nanoparticles

    International Nuclear Information System (INIS)

    Sengar, Saurabh K.; Mehta, B. R.; Govind

    2014-01-01

    In this report, X-ray photoelectron spectroscopy studies have been carried out on Pd, Ag, Cu, Pd-Ag, and Pd-Cu nanoparticles having identical sizes corresponding to mobility equivalent diameters of 60, 40, and 20 nm. The nanoparticles were prepared by the gas phase synthesis method. The effect of size on valence and core levels in metal and alloy nanoparticles has been studied by comparing the values to those with the 60 nm nanoparticles. The effect of alloying has been investigated by comparing the valence and core level binding energies of Pd-Cu and Pd-Ag alloy nanoparticles with the corresponding values for Pd, Ag, and Cu nanoparticles of identical sizes. These effects have been explained in terms of size induced lattice contractions, alloying induced charge transfer, and hybridization effects. The observation of alloying and size induced binding energy shifts in bimetallic nanoparticles is important from the point of view of hydrogen reactivity

  12. Observation of Rydberg transitions from the inner valence shell of ethane

    International Nuclear Information System (INIS)

    Dillon, M.A.; Tanaka, H.; Spence, D.

    1987-01-01

    The electron impact spectrum of ethane has been examined in a region that includes ionization out of the inner valence shell. One diffuse structure and a progression of ten vibrational bands have been found in a 4 eV range below and to some degree overlapping the 2 A 2 /sub u/ ion threshold. Evidence indicates that the observed transitions belong to the symmetry forbidden Rydberg series (2a 2 /sub u/) 2 →(2a 2 /sub u/, npσ or npπ)

  13. Study of band terminating in the A ≅ 100 by EUROGAM

    International Nuclear Information System (INIS)

    Gizon, J.; Gizon, A.; Genevey, J.; Santos, D.; Nyako, B.M.; Timar, J.; Zolnai, L.; Boston, A.J.; Zoss, D.T.; Paul, E.S.; Semple, A.T.; O'Brien, N.J.; Parry, C.M.; Cata-Danil, Gh.; Bucurescu, D.; Afanasjev, A.V.; Ragnarsson, I.

    1997-01-01

    Terminating bands in nuclei in the A≅ 100 region have been investigated using the EUROGAM2 array. Results have been obtained for Pd (Z 46) and Rh (Z = 45) isotopes. In the nucleus 102 Pd, eight terminating configurations are identified. It is the first nucleus where terminating bands built on the valence space configurations and on core excited configurations are observed. Terminating bands have been also found in 103 Pd and 102 Rh. For 102 Rh it is the first case of band terminations identified in a doubly-odd nucleus below the Z = 50 shell closure. (authors)

  14. Band-to-band transitions, selection rules, effective mass, and excitonic contributions in monoclinic β -Ga2O3

    Science.gov (United States)

    Mock, Alyssa; Korlacki, Rafał; Briley, Chad; Darakchieva, Vanya; Monemar, Bo; Kumagai, Yoshinao; Goto, Ken; Higashiwaki, Masataka; Schubert, Mathias

    2017-12-01

    We employ an eigenpolarization model including the description of direction dependent excitonic effects for rendering critical point structures within the dielectric function tensor of monoclinic β -Ga2O3 yielding a comprehensive analysis of generalized ellipsometry data obtained from 0.75-9 eV. The eigenpolarization model permits complete description of the dielectric response. We obtain, for single-electron and excitonic band-to-band transitions, anisotropic critical point model parameters including their polarization vectors within the monoclinic lattice. We compare our experimental analysis with results from density functional theory calculations performed using the Gaussian-attenuation-Perdew-Burke-Ernzerhof hybrid density functional. We present and discuss the order of the fundamental direct band-to-band transitions and their polarization selection rules, the electron and hole effective mass parameters for the three lowest band-to-band transitions, and their excitonic contributions. We find that the effective masses for holes are highly anisotropic and correlate with the selection rules for the fundamental band-to-band transitions. The observed transitions are polarized close to the direction of the lowest hole effective mass for the valence band participating in the transition.

  15. UV photo-detector based on p-NiO thin film/n-ZnO nanorods heterojunction prepared by a simple process

    International Nuclear Information System (INIS)

    Echresh, Ahmad; Chey, Chan Oeurn; Zargar Shoushtari, Morteza; Khranovskyy, Volodymyr; Nur, Omer; Willander, Magnus

    2015-01-01

    Highlights: • The p-NiO/n-ZnO heterojunction showed an obvious rectifying behavior and the response of the diode was excellent in generating photocurrent upon UV illumination. • Diode electrical performance presented here were superior to those achieved from similar heterojunction prepared by different methods. • The XPS results show that the heterojunction has a type-II band alignment with a valence band offset of 1.50 eV and conduction band offset of 1.83 eV. - Abstract: A UV photo-detector based on p-NiO thin film/n-ZnO nanorods heterojunction was fabricated using a simple two-step fabrication process. The aqueous chemical hydrothermal and thermal evaporation methods were combined to grow the ZnO nanorods and the NiO thin film, respectively. Structural investigation indicated that well aligned ZnO nanorods with hexagonal face having a preferential orientation along the c-axis (0 0 2) have been achieved and that the NiO thin film is covering all the ZnO nanorods. X-ray photoelectron spectroscopy (XPS) was used to investigate the band alignment of the heterojunction and the valence and the conduction band offsets were determined to be 1.50 eV and 1.83 eV, respectively. The current–voltage characteristics of the p-NiO thin film/ZnO nanorods heterojunction showed a clear rectifying behavior under both dark and UV illumination conditions. The response of the heterojunction diode was excellent regarding the photocurrent generation. Although other similar heterojunction diodes demonstrated lower threshold voltage, the rectification ratio and the sensitivity of the fabricated diode were superior in comparison to other similar heterojunctions reported recently, implying the vitality of the presented two-step process

  16. Unraveling the resistive switching effect in ZnO/0.5Ba(Zr{sub 0.2}Ti{sub 0.8})O{sub 3}-0.5(Ba{sub 0.7}Ca{sub 0.3})TiO{sub 3} heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Silva, J.P.B., E-mail: josesilva@fisica.uminho.pt [Centre of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga (Portugal); IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Departamento de Física e Astronomia, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto (Portugal); Vorokhta, M.; Dvořák, F. [Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 18000 Prague 8 (Czech Republic); Sekhar, K.C. [Centre of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga (Portugal); Department of Physics, School of Basic and Applied Science, Central University of Tamil Nadu, Thiruvarur 610 101 (India); Matolín, V. [Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 18000 Prague 8 (Czech Republic); Moreira, J. Agostinho [IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Departamento de Física e Astronomia, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto (Portugal); Pereira, M.; Gomes, M.J.M. [Centre of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga (Portugal)

    2017-04-01

    Highlights: • ZnO/0.5BZT-0.5BCT heterostructures exhibited resistive switching (RS) ratio ≥ 10 4. • Effect of oxygen pressure used in the deposition of ZnO on RS ratio is highlighted. • Determination of the Band alignment in ZnO/0.5BZT-0.5BCT heterojunctions from XPS. • Resistive Switching is explained based on charge coupling effect. - Abstract: This work reports the effect of partial oxygen pressure, used in the deposition of the ZnO layer, on the band alignment at ZnO – 0.5Ba(Zr{sub 0.2}Ti{sub 0.8})O{sub 3}-0.5(Ba{sub 0.7}Ca{sub 0.3})TiO{sub 3} (0.5BZT-0.5BCT) interface and on the resistive switching (RS) behavior of pulsed laser deposited ZnO/0.5BZT-0.5BCT heterostructures. X-ray photoelectron spectroscopy (XPS) has been employed to measure the valence band offset and the conduction band offset of the ZnO/0.5BZT-0.5BCT heterojunctions. The valence and conduction band offsets of the ZnO/0.5BZT-0.5BCT heterostucture with ZnO deposited at 10{sup −2} mbar of partial oxygen pressure were found to be 0.27 and 0.80 eV, respectively. The RS effect in heterostructures is explained on the base of the charge coupling between the switchable polarization of ferroelectric layer and the non-switchable polarization of semiconductor layer. The heterostructure with ZnO deposited at 10{sup −2} mbar of partial oxygen pressure displays optimum RS characteristics, with a switching ratio ≥ 10{sup 4} and excellent retention and endurance characteristics. The optimum RS characteristics are attributed to a good interface quality with enough carrier concentration in ZnO, as evidenced by XPS.

  17. Electronic band structure of Two-Dimensional WS2/Graphene van der Waals Heterostructures

    Science.gov (United States)

    Henck, Hugo; Ben Aziza, Zeineb; Pierucci, Debora; Laourine, Feriel; Reale, Francesco; Palczynski, Pawel; Chaste, Julien; Silly, Mathieu G.; Bertran, François; Le Fèvre, Patrick; Lhuillier, Emmanuel; Wakamura, Taro; Mattevi, Cecilia; Rault, Julien E.; Calandra, Matteo; Ouerghi, Abdelkarim

    2018-04-01

    Combining single-layer two-dimensional semiconducting transition-metal dichalcogenides (TMDs) with a graphene layer in van der Waals heterostructures offers an intriguing means of controlling the electronic properties through these heterostructures. Here, we report the electronic and structural properties of transferred single-layer W S2 on epitaxial graphene using micro-Raman spectroscopy, angle-resolved photoemission spectroscopy measurements, and density functional theory (DFT) calculations. The results show good electronic properties as well as a well-defined band arising from the strong splitting of the single-layer W S2 valence band at the K points, with a maximum splitting of 0.44 eV. By comparing our DFT results with local and hybrid functionals, we find the top valence band of the experimental heterostructure is close to the calculations for suspended single-layer W S2 . Our results provide an important reference for future studies of electronic properties of W S2 and its applications in valleytronic devices.

  18. The complex band structure for armchair graphene nanoribbons

    International Nuclear Information System (INIS)

    Zhang Liu-Jun; Xia Tong-Sheng

    2010-01-01

    Using a tight binding transfer matrix method, we calculate the complex band structure of armchair graphene nanoribbons. The real part of the complex band structure calculated by the transfer matrix method fits well with the bulk band structure calculated by a Hermitian matrix. The complex band structure gives extra information on carrier's decay behaviour. The imaginary loop connects the conduction and valence band, and can profoundly affect the characteristics of nanoscale electronic device made with graphene nanoribbons. In this work, the complex band structure calculation includes not only the first nearest neighbour interaction, but also the effects of edge bond relaxation and the third nearest neighbour interaction. The band gap is classified into three classes. Due to the edge bond relaxation and the third nearest neighbour interaction term, it opens a band gap for N = 3M − 1. The band gap is almost unchanged for N = 3M + 1, but decreased for N = 3M. The maximum imaginary wave vector length provides additional information about the electrical characteristics of graphene nanoribbons, and is also classified into three classes

  19. Band alignment of two-dimensional metal monochalcogenides MXs (M=Ga,In; X=S,Se,Te

    Directory of Open Access Journals (Sweden)

    Huazheng Sun

    2017-09-01

    Full Text Available Monolayer metal monochalcogenides MXs (M=Ga,In; X=S,Se,Te form a new class of two-dimensional semiconductors with indirect band gaps, and their band alignment information is investigated via first principles calculations. The dependence of band gap, valence-band maximum, conduction band minimum, and charge transfer on the M or X element has been obtained and can be understood from the orbital analysis of the band edges. Potential applications of metal monochalcogenides to design van der Waals heterostructures and catalyse the photo-splitting reaction of water have been discussed.

  20. Band-to-band tunneling distance analysis in the heterogate electron–hole bilayer tunnel field-effect transistor

    Energy Technology Data Exchange (ETDEWEB)

    Padilla, J. L., E-mail: jose.padilladelatorre@epfl.ch [Nanoelectronic Devices Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015 (Switzerland); Departamento de Electrónica y Tecnología de los Computadores, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada (Spain); Palomares, A. [Departamento de Matemática Aplicada, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada (Spain); Alper, C.; Ionescu, A. M. [Nanoelectronic Devices Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015 (Switzerland); Gámiz, F. [Departamento de Electrónica y Tecnología de los Computadores, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada (Spain)

    2016-01-28

    In this work, we analyze the behavior of the band-to-band tunneling distance between electron and hole subbands resulting from field-induced quantum confinement in the heterogate electron–hole bilayer tunnel field-effect transistor. We show that, analogously to the explicit formula for the tunneling distance that can be easily obtained in the semiclassical framework where the conduction and valence band edges are allowed states, an equivalent analytical expression can be derived in the presence of field-induced quantum confinement for describing the dependence of the tunneling distance on the body thickness and material properties of the channel. This explicit expression accounting for quantum confinement holds valid provided that the potential wells for electrons and holes at the top and bottom of the channel can be approximated by triangular profiles. Analytical predictions are compared to simulation results showing very accurate agreement.

  1. Valence skipping driven superconductivity and charge Kondo effect

    International Nuclear Information System (INIS)

    Yanagisawa, Takashi; Hase, Izumi

    2013-01-01

    Highlights: •Valence skipping in metallic compounds can give rise to an unconventional superconductivity. •Several elements in the periodic table show valence skipping (or valence missing), for example, Bi forms the compounds in valence states +3 and +5. •The doping of valence skipping elements will induce superconductivity and this will lead to a possibility of high temperature superconductivity. •We consider the Wolf model with negative-U impurities, and show a phase diagram including superconducting phase. •There is a high temperature region near the boundary. -- Abstract: Valence skipping in metallic compounds can give rise to an unconventional superconductivity. Several elements in the periodic table show valence skipping (or valence missing), for example, Bi forms the compounds in valence states +3 and +5. The doping of valence skipping elements will induce superconductivity and this will lead to a possibility of high temperature superconductivity. We consider the Wolf model with negative-U impurities, and show a phase diagram including superconducting phase. The superconducting state is changed into a metallic state with a local singlet as the attractive interaction |U| increases. There is a high temperature region near the boundary

  2. Simultaneous conditioning of valence and arousal.

    Science.gov (United States)

    Gawronski, Bertram; Mitchell, Derek G V

    2014-01-01

    Evaluative conditioning (EC) refers to the change in the valence of a conditioned stimulus (CS) due to its pairing with a positive or negative unconditioned stimulus (US). To the extent that core affect can be characterised by the two dimensions of valence and arousal, EC has important implications for the origin of affective responses. However, the distinction between valence and arousal is rarely considered in research on EC or conditioned responses more generally. Measuring the subjective feelings elicited by a CS, the results from two experiments showed that (1) repeated pairings of a CS with a positive or negative US of either high or low arousal led to corresponding changes in both CS valence and CS arousal, (2) changes in CS arousal, but not changes in CS valence, were significantly related to recollective memory for CS-US pairings, (3) subsequent presentations of the CS without the US reduced the conditioned valence of the CS, with conditioned arousal being less susceptible to extinction and (4) EC effects were stronger for high arousal than low arousal USs. The results indicate that the conditioning of affective responses can occur simultaneously along two independent dimensions, supporting evidence in related areas that calls for a consideration of both valence and arousal. Implications for research on EC and the acquisition of emotional dispositions are discussed.

  3. Great Apes and Biodiversity Offset Projects in Africa: The Case for National Offset Strategies

    Science.gov (United States)

    Kormos, Rebecca; Kormos, Cyril F.; Humle, Tatyana; Lanjouw, Annette; Rainer, Helga; Victurine, Ray; Mittermeier, Russell A.; Diallo, Mamadou S.; Rylands, Anthony B.; Williamson, Elizabeth A.

    2014-01-01

    The development and private sectors are increasingly considering “biodiversity offsets” as a strategy to compensate for their negative impacts on biodiversity, including impacts on great apes and their habitats in Africa. In the absence of national offset policies in sub-Saharan Africa, offset design and implementation are guided by company internal standards, lending bank standards or international best practice principles. We examine four projects in Africa that are seeking to compensate for their negative impacts on great ape populations. Our assessment of these projects reveals that not all apply or implement best practices, and that there is little standardization in the methods used to measure losses and gains in species numbers. Even if they were to follow currently accepted best-practice principles, we find that these actions may still fail to contribute to conservation objectives over the long term. We advocate for an alternative approach in which biodiversity offset and compensation projects are designed and implemented as part of a National Offset Strategy that (1) takes into account the cumulative impacts of development in individual countries, (2) identifies priority offset sites, (3) promotes aggregated offsets, and (4) integrates biodiversity offset and compensation projects with national biodiversity conservation objectives. We also propose supplementary principles necessary for biodiversity offsets to contribute to great ape conservation in Africa. Caution should still be exercised, however, with regard to offsets until further field-based evidence of their effectiveness is available. PMID:25372894

  4. Study of band terminating in the A {approx_equal} 100 by EUROGAM; Recherche de terminaisons de bandes dans la region A {approx_equal} 100 avec EUROGAM

    Energy Technology Data Exchange (ETDEWEB)

    Gizon, J.; Gizon, A.; Genevey, J.; Santos, D. [Inst. des Sciences Nucleaires, Grenoble-1 Univ., 38 (France); Nyako, B.M.; Timar, J.; Zolnai, L. [Institute of Nuclear Research, Debrecen (Hungary); Boston, A.J.; Zoss, D.T.; Paul, E.S.; Semple, A.T. [Oliver Lodge Laboratory, University of Liverpool, Liverpool (United Kingdom); O`Brien, N.J.; Parry, C.M. [Department of Physics, University of York, Heslington, York (United Kingdom); Cata-Danil, Gh.; Bucurescu, D. [Horia Hulubei Institute of Physics and Nuclear Engineering, Bucharest (Romania); Afanasjev, A.V.; Ragnarsson, I. [Department of Mathematical Physics, University of Lund, Lund (Sweden)

    1997-12-31

    Terminating bands in nuclei in the A{approx_equal} 100 region have been investigated using the EUROGAM2 array. Results have been obtained for Pd (Z 46) and Rh (Z = 45) isotopes. In the nucleus {sup 102}Pd, eight terminating configurations are identified. It is the first nucleus where terminating bands built on the valence space configurations and on core excited configurations are observed. Terminating bands have been also found in {sup 103}Pd and {sup 102}Rh. For {sup 102}Rh it is the first case of band terminations identified in a doubly-odd nucleus below the Z = 50 shell closure. (authors) 9 refs., 2 figs.

  5. Strain effects in the common-cation II-VI heterostructures: case of ZnS/ZnSe superlattices

    CERN Document Server

    Tit, N

    2003-01-01

    The electronic band-structures of the strained-layer ZnS/ZnSe (001) superlattices (SLs) have been investigated using the sp sup 3 s* tight-binding method, which includes the strain and spin-orbit effects. The SL band-structures are studied versus the biaxial strain, layer thickness, and band offsets. The results suggest that the common-cation II-VI heterojunction exhibit a vanishingly small conduction-band offset (CBO). It is shown that the SL valence-band top state is always a heavy-hole localized within ZnSe slabs; whereas the conduction-band edge state (electron) is sensitive to the biaxial strain (or VBO). To assess the strain effects, we considered three differently strained SLs corresponding to the three substrates: (i) ZnSe; (ii) ZnS sub 0 sub . sub 5 Se sub 0 sub . sub 5; and (iii) ZnS. The results show that all the studied SLs are of type-I except those strained to ZnS (case iii), that may exhibit type-I to type-II transition. One striking result obtained here is the existence of a critical VBO (V su...

  6. Band termination in the N=Z nucleus 44Ti

    International Nuclear Information System (INIS)

    Ur, C.A.; Lenzi, S.M.; Martinez-Pinedo, G.

    1998-01-01

    Nuclei in the vicinity of the middle of the 1f 7/2 shell show strong prolate deformation at low spins resulting in rotational-like band structures. With increasing angular momentum the structure of these nuclei evolves through triaxial and spherical shapes. Recently, band terminating states corresponding to fully aligned configurations of valence nucleons in the f 7/2 shell have been reported. Further increase of the angular momentum can be achieved by particle excitations on the higher shell. This will result in high energy γ-ray transitions as it was observed in 50 Cr. We have investigated the structure of 44 Ti up to the band termination. Excited states in 44 Ti have been populated via the 28 Si + 24 Mg at 110 MeV beam energy. The target consisted of ∼0.5 mg/cm 2 of 24 Mg deposited on a gold backing. Gamma-rays were detected with the GASP multidetector array composed by 40 HPGe Compton-suppressed detectors and the inner ball built of 80 BGO detectors. The preliminary level scheme of 44 Ti, as determined in our work, is presented. This nucleus has 2 valence protons and 2 valence neutrons filling the f 7/2 shell. The band terminating state corresponding to their total alignment is the 12 + state. Several γ-rays transitions above this state have been identified. Also, we have identified two negative parity bands strongly connected to the yrast positive parity structure. Such structures have also been observed in other two even-even N=Z nuclei in the f 7/2 shell, namely, 44 Cr and 52 Fe, but they were less populated. The structure of 44 Ti is also interesting from the point of view of the cross-conjugate symmetry. Comparing the level structure of 44 Ti and the one of its cross-conjugate nucleus at the other end of the shell, 52 Fe, it can be noticed that up to spin 10ℎ their structure is very similar, but in 44 Ti the band terminating state 12 + is not below the 10 + state as in the case of 52 Fe. This was related to a reminiscent degree of collectivity in the

  7. Band-to-band and inner shell excitation VIS-UV photoluminescence of quaternary InAlGaN alloys

    International Nuclear Information System (INIS)

    Fukui, K.; Naoe, S.; Okada, K.; Hamada, S.; Hirayama, H.

    2006-01-01

    Visible and ultraviolet photoluminescence and photoluminescence excitation spectra of quaternary InAlGaN alloys were measured. The excitation photon energy covers from band edge to 180 eV, near both nitrogen K (∝400 eV) and aluminium K (∝1.5 keV) inner shell energy region. From photoluminescence excitation spectra photoluminescence intensity per incident photon number varies in proportion to incident photon energy. This result implies that many conduction band electron - valence band hole pairs which are responsible for photoluminescence are produced by high energy excitation. Time resolved decay curves were also measured in the same energy region. No effect of high energy excitation on time resolved decay measurements suggests a role of indium on the photoluminescence mechanism in InAlGaN system. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Quasiparticle excitations in valence-fluctuation materials: effects of band structure and crystal fields

    International Nuclear Information System (INIS)

    Brandow, B.H.

    1985-01-01

    Evidence is now quite strong that the elementary hybridization model is the correct way to understand the lattice-coherent Fermi liquid regime at very low temperatures. Many-body theory leads to significant renormalizations of the input parameters, and many of the band-theoretic channels for hybridization are suppressed by the combined effects of Hund's-rule coupling, crystal-field splitting, and the f-f Coulomb repulsion U. Some exploratory calculations based on this picture are described, and some inferences are drawn about the band structures of several heavy-fermion materials. These inferences can and should be tested by suitably modified band-theoretic calculations. We find evidence for a significant Baber-scattering contribution in the very-low-temperature resistivity. A new mechanism is proposed for crossover from the coherent Fermi-liquid regime to the incoherent dense-Kondo regime. 28 refs

  9. Dirac Cones, Topological Edge States, and Nontrivial Flat Bands in Two-Dimensional Semiconductors with a Honeycomb Nanogeometry

    Directory of Open Access Journals (Sweden)

    E. Kalesaki

    2014-01-01

    Full Text Available We study theoretically two-dimensional single-crystalline sheets of semiconductors that form a honeycomb lattice with a period below 10 nm. These systems could combine the usual semiconductor properties with Dirac bands. Using atomistic tight-binding calculations, we show that both the atomic lattice and the overall geometry influence the band structure, revealing materials with unusual electronic properties. In rocksalt Pb chalcogenides, the expected Dirac-type features are clouded by a complex band structure. However, in the case of zinc-blende Cd-chalcogenide semiconductors, the honeycomb nanogeometry leads to rich band structures, including, in the conduction band, Dirac cones at two distinct energies and nontrivial flat bands and, in the valence band, topological edge states. These edge states are present in several electronic gaps opened in the valence band by the spin-orbit coupling and the quantum confinement in the honeycomb geometry. The lowest Dirac conduction band has S-orbital character and is equivalent to the π-π^{⋆} band of graphene but with renormalized couplings. The conduction bands higher in energy have no counterpart in graphene; they combine a Dirac cone and flat bands because of their P-orbital character. We show that the width of the Dirac bands varies between tens and hundreds of meV. These systems emerge as remarkable platforms for studying complex electronic phases starting from conventional semiconductors. Recent advancements in colloidal chemistry indicate that these materials can be synthesized from semiconductor nanocrystals.

  10. Band alignment and interfacial chemical structure of the HfLaO/InGaZnO4 heterojunction investigated by x-ray photoelectron spectroscopy

    International Nuclear Information System (INIS)

    Qian, Ling-Xuan; Wu, Ze-Han; Zhang, Yi-Yu; Liu, Xing-Zhao; Li, Yan-Rong; Liu, Yuan; Song, Jia-Qi

    2017-01-01

    Amorphous InGaZnO 4 thin film transistors (a-IGZO TFTs) with HfLaO gate dielectrics have been widely demonstrated to possess extremely excellent electrical characteristics, and thus show great potential for applications in various next-generation electronic products. Nevertheless, the in-depth understanding of HfLaO/IGZO interfacial features is still lacking, which makes further device optimization lack clear guidance. In this work, the band alignment and interfacial chemical structure of a sputtering-prepared HfLaO/IGZO heterojunction was investigated through x-ray photoelectron spectroscopy. The valence and conduction band offsets (Δ E v and Δ E c ) at the interface were determined to be 0.57 eV and 1.48 eV, respectively. The relatively large Δ E v is mainly attributed to the formation of the interfacial layer (IL) and thus the upward band bending from IGZO to the surface of HfLaO. Furthermore, it was found that the oxygen vacancies on the surface of IGZO were significantly suppressed upon the deposition of HfLaO, which not only explained the previously reported ultrahigh performance of a-IGZO/HfLaO TFTs to some extent, but also additionally validated the formation of the IL. Our findings have successfully revealed the importance of ILs in modifying the band alignment and interfacial trap states of HfLaO/IGZO heterojunctions, thus suggesting a potential route to further optimizing a-IGZO/HfLaO TFTs so as to satisfy the requirements of next-generation technologies. (paper)

  11. Thermoelectric band engineering: The role of carrier scattering

    Science.gov (United States)

    Witkoske, Evan; Wang, Xufeng; Lundstrom, Mark; Askarpour, Vahid; Maassen, Jesse

    2017-11-01

    Complex electronic band structures, with multiple valleys or bands at the same or similar energies, can be beneficial for thermoelectric performance, but the advantages can be offset by inter-valley and inter-band scattering. In this paper, we demonstrate how first-principles band structures coupled with recently developed techniques for rigorous simulation of electron-phonon scattering provide the capabilities to realistically assess the benefits and trade-offs associated with these materials. We illustrate the approach using n-type silicon as a model material and show that intervalley scattering is strong. This example shows that the convergence of valleys and bands can improve thermoelectric performance, but the magnitude of the improvement depends sensitively on the relative strengths of intra- and inter-valley electron scattering. Because anisotropy of the band structure also plays an important role, a measure of the benefit of band anisotropy in the presence of strong intervalley scattering is presented.

  12. Electronic band structure of magnetic bilayer graphene superlattices

    International Nuclear Information System (INIS)

    Pham, C. Huy; Nguyen, T. Thuong; Nguyen, V. Lien

    2014-01-01

    Electronic band structure of the bilayer graphene superlattices with δ-function magnetic barriers and zero average magnetic flux is studied within the four-band continuum model, using the transfer matrix method. The periodic magnetic potential effects on the zero-energy touching point between the lowest conduction and the highest valence minibands of pristine bilayer graphene are exactly analyzed. Magnetic potential is shown also to generate the finite-energy touching points between higher minibands at the edges of Brillouin zone. The positions of these points and the related dispersions are determined in the case of symmetric potentials.

  13. Bands dispersion and charge transfer in β-BeH2

    Science.gov (United States)

    Trivedi, D. K.; Galav, K. L.; Joshi, K. B.

    2018-04-01

    Predictive capabilities of ab-initio method are utilised to explore bands dispersion and charge transfer in β-BeH2. Investigations are carried out using the linear combination of atomic orbitals method at the level of density functional theory. The crystal structure and related parameters are settled by coupling total energy calculations with the Murnaghan equation of state. Electronic bands dispersion from PBE-GGA is reported. The PBE-GGA, and PBE0 hybrid functional, show that β-BeH2 is a direct gap semiconductor with 1.18 and 2.40 eV band gap. The band gap slowly decreases with pressure and beyond l00 GPa overlap of conduction and valence bands at the r point is observed. Charge transfer is studied by means of Mullikan population analysis.

  14. Valence effects on adsorption: a preliminary assessment of the effects on valence state control on sorption measurements

    International Nuclear Information System (INIS)

    Meyer, R.E.; Arnold, W.D.; Case, F.; Shiao, S.Y.; Palmer, D.A.

    1983-01-01

    Electrochemical arguments are advanced to illustrate that what is usually measured in practice is a mixed potential determined by the kinetics of the electrode processes occurring at the indicator electrode. Valence states can be altered electrochemically or by use of added chemical reagents, including redox couples which can hold the potential to relatively specific potentials. The disadvantage of added chemical reagents is that they may alter the characteristics of the sorption reactions by interaction with the sorbent. Electrochemical methods are versatile and do not add reagents, but in some caes the nuclide can adsorb on the electrode itself. A description is given of the application of the electrochemical method of valence control to determination of sorption of Np(V) on alumina. Valence state control and analysis can be used to study possible redox reactions on materials which might be used as backfill materials. A description is given of survey experiments with a number of sulfides and iron-containing materials. Valence state analysis is used on the initial solutions and leachate from acid leaches of the sorbent after the sorption experiment to help determine whether valence state change is occurring. The preliminary results indicate that on the sulfides tested, sorption occurs both with and without valence state change

  15. Rotational bands terminating at maximal spin in the valence space

    Energy Technology Data Exchange (ETDEWEB)

    Ragnarsson, I.; Afanasjev, A.V. [Lund Institute of Technology (Sweden)

    1996-12-31

    For nuclei with mass A {le} 120, the spin available in {open_quotes}normal deformation configurations{close_quotes} is experimentally accessible with present detector systems. Of special interest are the nuclei which show collective features at low or medium-high spin and where the corresponding rotational bands with increasing spin can be followed in a continuous way to or close to a non-collective terminating state. Some specific features in this context are discussed for nuclei in the A = 80 region and for {sup 117,118}Xe.

  16. Determination of the surface band bending in InxGa1−xN films by hard x-ray photoemission spectroscopy

    Directory of Open Access Journals (Sweden)

    Mickael Lozac'h, Shigenori Ueda, Shitao Liu, Hideki Yoshikawa, Sang Liwen, Xinqiang Wang, Bo Shen, Kazuaki Sakoda, Keisuke Kobayashi and Masatomo Sumiya

    2013-01-01

    Full Text Available Core-level and valence band spectra of InxGa1−xN films were measured using hard x-ray photoemission spectroscopy (HX-PES. Fine structure, caused by the coupling of the localized Ga 3d and In 4d with N 2s states, was experimentally observed in the films. Because of the large detection depth of HX-PES (~20 nm, the spectra contain both surface and bulk information due to the surface band bending. The InxGa1−xN films (x = 0–0.21 exhibited upward surface band bending, and the valence band maximum was shifted to lower binding energy when the mole fraction of InN was increased. On the other hand, downward surface band bending was confirmed for an InN film with low carrier density despite its n-type conduction. Although the Fermi level (EF near the surface of the InN film was detected inside the conduction band as reported previously, it can be concluded that EF in the bulk of the film must be located in the band gap below the conduction band minimum.

  17. Development of GaInNAsSb alloys: Growth, band structure, optical properties and applications

    International Nuclear Information System (INIS)

    Harris, James S. Jr.; Kudrawiec, R.; Yuen, H.B.; Bank, S.R.; Bae, H.P.; Wistey, M.A.; Jackrel, D.; Pickett, E.R.; Sarmiento, T.; Goddard, L.L.; Lordi, V.; Gugov, T.

    2007-01-01

    In the past few years, GaInNAsSb has been found to be a potentially superior material to both GaInNAs and InGaAsP for communications wavelength laser applications. It has been observed that due to the surfactant role of antimony during epitaxy, higher quality material can be grown over the entire 1.2-1.6 μm range on GaAs substrates. In addition, it has been discovered that antimony in GaInNAsSb also works as a constituent that significantly modifies the valence band. These findings motivated a systematic study of GaInNAsSb alloys with widely varying compositions. Our recent progress in growth and materials development of GaInNAsSb alloys and our fabrication of 1.5-1.6 μm lasers are discussed in this paper. We review our recent studies of the conduction band offset in (Ga,In) (N,As,Sb)/GaAs quantum wells and discuss the growth challenges of GaInNAsSb alloys. Finally, we report record setting long wavelength edge emitting lasers and the first monolithic VCSELs operating at 1.5 μm based on GaInNAsSb QWs grown on GaAs. Successful development of GaInNAsSb alloys for lasers has led to a much broader range of potential applications for this material including: solar cells, electroabsorption modulators, saturable absorbers and far infrared optoelectronic devices and these are also briefly discussed in this paper. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  18. Development of GaInNAsSb alloys: Growth, band structure, optical properties and applications

    Energy Technology Data Exchange (ETDEWEB)

    Harris, James S. Jr.; Kudrawiec, R.; Yuen, H.B.; Bank, S.R.; Bae, H.P.; Wistey, M.A.; Jackrel, D.; Pickett, E.R.; Sarmiento, T.; Goddard, L.L.; Lordi, V.; Gugov, T. [Solid State and Photonics Laboratory, Stanford University, CIS-X 328, Via Ortega, Stanford, California 94305-4075 (United States)

    2007-08-15

    In the past few years, GaInNAsSb has been found to be a potentially superior material to both GaInNAs and InGaAsP for communications wavelength laser applications. It has been observed that due to the surfactant role of antimony during epitaxy, higher quality material can be grown over the entire 1.2-1.6 {mu}m range on GaAs substrates. In addition, it has been discovered that antimony in GaInNAsSb also works as a constituent that significantly modifies the valence band. These findings motivated a systematic study of GaInNAsSb alloys with widely varying compositions. Our recent progress in growth and materials development of GaInNAsSb alloys and our fabrication of 1.5-1.6 {mu}m lasers are discussed in this paper. We review our recent studies of the conduction band offset in (Ga,In) (N,As,Sb)/GaAs quantum wells and discuss the growth challenges of GaInNAsSb alloys. Finally, we report record setting long wavelength edge emitting lasers and the first monolithic VCSELs operating at 1.5 {mu}m based on GaInNAsSb QWs grown on GaAs. Successful development of GaInNAsSb alloys for lasers has led to a much broader range of potential applications for this material including: solar cells, electroabsorption modulators, saturable absorbers and far infrared optoelectronic devices and these are also briefly discussed in this paper. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. The voluntary offset - approaches and limitations

    International Nuclear Information System (INIS)

    2012-06-01

    After having briefly presented the voluntary offset mechanism which aims at funding a project of reduction or capture of greenhouse gas emissions, this document describes the approach to be followed to adopt this voluntary offset, for individuals as well as for companies, communities or event organisations. It describes other important context issues (projects developed under the voluntary offset, actors of the voluntary offsetting market, market status, offset labels), and how to proceed in practice (definition of objectives and expectations, search for needed requirements, to ensure the meeting of requirements with respect to expectations). It addresses the case of voluntary offset in France (difficult implantation, possible solutions)

  20. Human Amygdala Represents the Complete Spectrum of Subjective Valence

    Science.gov (United States)

    Jin, Jingwen; Zelano, Christina; Gottfried, Jay A.

    2015-01-01

    Although the amygdala is a major locus for hedonic processing, how it encodes valence information is poorly understood. Given the hedonic potency of odor stimuli and the amygdala's anatomical proximity to the peripheral olfactory system, we combined high-resolution fMRI with pattern-based multivariate techniques to examine how valence information is encoded in the amygdala. Ten human subjects underwent fMRI scanning while smelling 9 odorants that systematically varied in perceived valence. Representational similarity analyses showed that amygdala codes the entire dimension of valence, ranging from pleasantness to unpleasantness. This unidimensional representation significantly correlated with self-reported valence ratings but not with intensity ratings. Furthermore, within-trial valence representations evolved over time, prioritizing earlier differentiation of unpleasant stimuli. Together, these findings underscore the idea that both spatial and temporal features uniquely encode pleasant and unpleasant odor valence in the amygdala. The availability of a unidimensional valence code in the amygdala, distributed in both space and time, would create greater flexibility in determining the pleasantness or unpleasantness of stimuli, providing a mechanism by which expectation, context, attention, and learning could influence affective boundaries for guiding behavior. SIGNIFICANCE STATEMENT Our findings elucidate the mechanisms of affective processing in the amygdala by demonstrating that this brain region represents the entire valence dimension from pleasant to unpleasant. An important implication of this unidimensional valence code is that pleasant and unpleasant valence cannot coexist in the amygdale because overlap of fMRI ensemble patterns for these two valence extremes obscures their unique content. This functional architecture, whereby subjective valence maps onto a pattern continuum between pleasant and unpleasant poles, offers a robust mechanism by which context

  1. Pressure variation of the valence band width in Ge: A self-consistent GW study

    DEFF Research Database (Denmark)

    Modak, Paritosh; Svane, Axel; Christensen, Niels Egede

    2009-01-01

    . In the present work we report results of quasiparticle self-consistent GW  (QSGW) band calculations for diamond- as well as β-tin-type Ge under pressure. For both phases we find that the band width increases with pressure. For β-tin Ge this agrees with experiment and density-functional theory, but for diamond Ge...

  2. On the electrical conductivity for the mixed-valence model with d-f correlations

    International Nuclear Information System (INIS)

    Borgiel, W.; Matlak, M.

    1984-08-01

    The static electrical conductivity of mixed-valence systems is calculated in the model of Matlak and Nolting [Solid State Commun., 47, 11 (1983); Z. Phys., B55, 103 (1984)]. The method takes into account the atomic properties more exactly than those connected with bands, and hence emphasizes the ionic aspect of the problem in some way; indeed, the calculations overestimate the atomic properties. Some results are presented in a graph. It is found that the electrical conductivity depends strongly on temperature and the electron-hole attraction constant

  3. A GPS Satellite Clock Offset Prediction Method Based on Fitting Clock Offset Rates Data

    Directory of Open Access Journals (Sweden)

    WANG Fuhong

    2016-12-01

    Full Text Available It is proposed that a satellite atomic clock offset prediction method based on fitting and modeling clock offset rates data. This method builds quadratic model or linear model combined with periodic terms to fit the time series of clock offset rates, and computes the model coefficients of trend with the best estimation. The clock offset precisely estimated at the initial prediction epoch is directly adopted to calculate the model coefficient of constant. The clock offsets in the rapid ephemeris (IGR provided by IGS are used as modeling data sets to perform certain experiments for different types of GPS satellite clocks. The results show that the clock prediction accuracies of the proposed method for 3, 6, 12 and 24 h achieve 0.43, 0.58, 0.90 and 1.47 ns respectively, which outperform the traditional prediction method based on fitting original clock offsets by 69.3%, 61.8%, 50.5% and 37.2%. Compared with the IGU real-time clock products provided by IGS, the prediction accuracies of the new method have improved about 15.7%, 23.7%, 27.4% and 34.4% respectively.

  4. 7 CFR 400.129 - Salary offset.

    Science.gov (United States)

    2010-01-01

    ... 7 Agriculture 6 2010-01-01 2010-01-01 false Salary offset. 400.129 Section 400.129 Agriculture... Years § 400.129 Salary offset. (a) Debt collection by salary offset is feasible if: the cost to the Government of collection by salary offset does not exceed the amount of the debt; there are no legal...

  5. Electronic structure calculations on nitride semiconductors and their alloys

    International Nuclear Information System (INIS)

    Dugdale, D.

    2000-09-01

    Calculations of the electronic properties of AIN, GaN, InN and their alloys are presented. Initial calculations are performed using the first principles pseudopotential method to obtain accurate lattice constants. Further calculations then investigate bonding in the nitrides through population analysis and density of state calculations. The empirical pseudopotential method is also used in this work. Pseudopotentials for each of the nitrides are constructed using a functional form that allows strained material and alloys to be studied. The conventional k.p valence band parameters for both zincblende and wurtzite are obtained from the empirical band structure using two different methods. A Monte-Carlo fitting of the k.p band structure to the pseudopotential data (or an effective mass method for the zincblende structure) is used to produce one set. Another set is obtained directly from the momentum matrix elements and energy eigenvalues at the centre of the Brillouin zone. Both methods of calculating k.p parameters produce band structure in excellent agreement with the original empirical band calculations near the centre of the Brillouin zone. The advantage of the direct method is that it produces consistent sets of parameters, and can be used in studies involving a series of alloy compositions. Further empirical pseudopotential method calculations are then performed for alloys of the nitrides. In particular, the variation of the band gap with alloy composition is investigated, and good agreement with theory and experiment is found. The direct method is used to obtain k.p parameters for the alloys, and is contrasted with the fitting approach. The behaviour of the nitrides under strain is also studied. In particular. valence band offsets for nitride heterojunctions are calculated, and a strong forward- backward asymmetry in the band offset is found, in good agreement with other results in the literature. (author)

  6. In-Band Interference Effects on UTRA LTE Uplink Resource Block Allocation

    DEFF Research Database (Denmark)

    Priyanto, Basuki Endah; Sørensen, Troels Bundgaard; Jensen, Ole Kiel

    2008-01-01

    In this paper we investigate the impact of in-band interference on the uplink multiple access of UMTS Terrestrial Radio Access, long term evolution (UTRA LTE). In- band and out-of-band interference arise as a result of transmitter imperfections. Out-of- band, or adjacent channel, interference can......, and when the interfering signal is received at higher power spectral density (PSD). The effect of frequency offset and different PSD level from the UE interferers to a victim UE is studied. The impact on different UE resource block size allocation is also investigated. The results are obtained from an LTE...

  7. Absence of paired crossing in the positive parity bands of 124Cs

    Science.gov (United States)

    Singh, A. K.; Basu, A.; Nag, Somnath; Hübel, H.; Domscheit, J.; Ragnarsson, I.; Al-Khatib, A.; Hagemann, G. B.; Herskind, B.; Elema, D. R.; Wilson, J. N.; Clark, R. M.; Cromaz, M.; Fallon, P.; Görgen, A.; Lee, I.-Y.; Ward, D.; Ma, W. C.

    2018-02-01

    High-spin states in 124Cs were populated in the 64Ni(64Ni,p 3 n ) reaction and the Gammasphere detector array was used to measure γ -ray coincidences. Both positive- and negative-parity bands, including bands with chiral configurations, have been extended to higher spin, where a shape change has been observed. The configurations of the bands before and after the alignment are discussed within the framework of the cranked Nilsson-Strutinsky model. The calculations suggest that the nucleus undergoes a shape transition from triaxial to prolate around spin I ≃22 of the positive-parity states. The alignment gain of 8 ℏ , observed in the positive-parity bands, is due to partial alignment of several valence nucleons. This indicates the absence of band crossing due to paired nucleons in the bands.

  8. Emotional valence and the free-energy principle.

    Science.gov (United States)

    Joffily, Mateus; Coricelli, Giorgio

    2013-01-01

    The free-energy principle has recently been proposed as a unified Bayesian account of perception, learning and action. Despite the inextricable link between emotion and cognition, emotion has not yet been formulated under this framework. A core concept that permeates many perspectives on emotion is valence, which broadly refers to the positive and negative character of emotion or some of its aspects. In the present paper, we propose a definition of emotional valence in terms of the negative rate of change of free-energy over time. If the second time-derivative of free-energy is taken into account, the dynamics of basic forms of emotion such as happiness, unhappiness, hope, fear, disappointment and relief can be explained. In this formulation, an important function of emotional valence turns out to regulate the learning rate of the causes of sensory inputs. When sensations increasingly violate the agent's expectations, valence is negative and increases the learning rate. Conversely, when sensations increasingly fulfil the agent's expectations, valence is positive and decreases the learning rate. This dynamic interaction between emotional valence and learning rate highlights the crucial role played by emotions in biological agents' adaptation to unexpected changes in their world.

  9. Emotional valence and the free-energy principle.

    Directory of Open Access Journals (Sweden)

    Mateus Joffily

    Full Text Available The free-energy principle has recently been proposed as a unified Bayesian account of perception, learning and action. Despite the inextricable link between emotion and cognition, emotion has not yet been formulated under this framework. A core concept that permeates many perspectives on emotion is valence, which broadly refers to the positive and negative character of emotion or some of its aspects. In the present paper, we propose a definition of emotional valence in terms of the negative rate of change of free-energy over time. If the second time-derivative of free-energy is taken into account, the dynamics of basic forms of emotion such as happiness, unhappiness, hope, fear, disappointment and relief can be explained. In this formulation, an important function of emotional valence turns out to regulate the learning rate of the causes of sensory inputs. When sensations increasingly violate the agent's expectations, valence is negative and increases the learning rate. Conversely, when sensations increasingly fulfil the agent's expectations, valence is positive and decreases the learning rate. This dynamic interaction between emotional valence and learning rate highlights the crucial role played by emotions in biological agents' adaptation to unexpected changes in their world.

  10. Ab initio valence calculations in chemistry

    CERN Document Server

    Cook, D B

    1974-01-01

    Ab Initio Valence Calculations in Chemistry describes the theory and practice of ab initio valence calculations in chemistry and applies the ideas to a specific example, linear BeH2. Topics covered include the Schrödinger equation and the orbital approximation to atomic orbitals; molecular orbital and valence bond methods; practical molecular wave functions; and molecular integrals. Open shell systems, molecular symmetry, and localized descriptions of electronic structure are also discussed. This book is comprised of 13 chapters and begins by introducing the reader to the use of the Schrödinge

  11. Band model for d- and f-metals

    International Nuclear Information System (INIS)

    Koelling, D.D.

    1982-01-01

    The application of band theory to metallic systems with d- and f-orbitals in the valence and conduction bands is discussed. Because such an application pushes theory and technique to their limits, several important features are briefly recapitulated. Within the transition metal systems, the elemental systems are used to discuss the fundamental formalism being applied and the newer directions into more complex systems are mentioned. Here we focus more on anisotropic properties and Fermi surface properties. Within the f-orbital systems, the focus is more on Ce and its compounds because of current interest with a relatively brief discussion of the actinides. the point of view advanced, however, has its origins in actinide research

  12. Metal-like Band Structures of Ultrathin Si {111} and {112} Surface Layers Revealed through Density Functional Theory Calculations.

    Science.gov (United States)

    Tan, Chih-Shan; Huang, Michael H

    2017-09-04

    Density functional theory calculations have been performed on Si (100), (110), (111), and (112) planes with tunable number of planes for evaluation of their band structures and density of states profiles. The purpose is to see whether silicon can exhibit facet-dependent properties derived from the presence of a thin surface layer having different band structures. No changes have been observed for single to multiple layers of Si (100) and (110) planes with a consistent band gap between the valence band and the conduction band. However, for 1, 2, 4, and 5 Si (111) and (112) planes, metal-like band structures were obtained with continuous density of states going from the valence band to the conduction band. For 3, 6, and more Si (111) planes, as well as 3 and 6 Si (112) planes, the same band structure as that seen for Si (100) and (110) planes has been obtained. Thus, beyond a layer thickness of five Si (111) planes at ≈1.6 nm, normal semiconductor behavior can be expected. The emergence of metal-like band structures for the Si (111) and (112) planes are related to variation in Si-Si bond length and bond distortion plus 3s and 3p orbital electron contributions in the band structure. This work predicts possession of facet-dependent electrical properties of silicon with consequences in FinFET transistor design. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Energetics of discrete selectivity bands and mutation-induced transitions in the calcium-sodium ion channels family.

    Science.gov (United States)

    Kaufman, I; Luchinsky, D G; Tindjong, R; McClintock, P V E; Eisenberg, R S

    2013-11-01

    We use Brownian dynamics (BD) simulations to study the ionic conduction and valence selectivity of a generic electrostatic model of a biological ion channel as functions of the fixed charge Q(f) at its selectivity filter. We are thus able to reconcile the discrete calcium conduction bands recently revealed in our BD simulations, M0 (Q(f)=1e), M1 (3e), M2 (5e), with a set of sodium conduction bands L0 (0.5e), L1 (1.5e), thereby obtaining a completed pattern of conduction and selectivity bands vs Q(f) for the sodium-calcium channels family. An increase of Q(f) leads to an increase of calcium selectivity: L0 (sodium-selective, nonblocking channel) → M0 (nonselective channel) → L1 (sodium-selective channel with divalent block) → M1 (calcium-selective channel exhibiting the anomalous mole fraction effect). We create a consistent identification scheme where the L0 band is putatively identified with the eukaryotic sodium channel The scheme created is able to account for the experimentally observed mutation-induced transformations between nonselective channels, sodium-selective channels, and calcium-selective channels, which we interpret as transitions between different rows of the identification table. By considering the potential energy changes during permeation, we show explicitly that the multi-ion conduction bands of calcium and sodium channels arise as the result of resonant barrierless conduction. The pattern of periodic conduction bands is explained on the basis of sequential neutralization taking account of self-energy, as Q(f)(z,i)=ze(1/2+i), where i is the order of the band and z is the valence of the ion. Our results confirm the crucial influence of electrostatic interactions on conduction and on the Ca(2+)/Na(+) valence selectivity of calcium and sodium ion channels. The model and results could be also applicable to biomimetic nanopores with charged walls.

  14. Crystal structure and band gap determination of HfO2 thin films

    NARCIS (Netherlands)

    Cheynet, M.C.; Pokrant, S.; Tichelaar, F.D.; Rouvière, J.L.

    2007-01-01

    Valence electron energy loss spectroscopy (VEELS) and high resolution transmission electron microscopy (HRTEM) are performed on three different HfO2 thin films grown on Si (001) by chemical vapor deposition (CVD) or atomic layer deposition (ALD). For each sample the band gap (Eg) is determined by

  15. Terahertz emission from CdHgTe/HgTe quantum wells with an inverted band structure

    Energy Technology Data Exchange (ETDEWEB)

    Vasilyev, Yu. B., E-mail: Yu.Vasilyev@mail.ioffe.ru [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Mikhailov, N. N. [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Vasilyeva, G. Yu.; Ivánov, Yu. L.; Zakhar’in, A. O.; Andrianov, A. V. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Vorobiev, L. E.; Firsov, D. A. [Peter the Great Saint-Petersburg Polytechnic University (Russian Federation); Grigoriev, M. N. [Ustinov Baltic State Technical University “VOENMEKh” (Russian Federation); Antonov, A. V.; Ikonnikov, A. V.; Gavrilenko, V. I. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

    2016-07-15

    The terahertz electroluminescence from Cd{sub 0.7}Hg{sub 0.3}Te/HgTe quantum wells with an inverted band structure in lateral electric fields is experimentally detected and studied. The emission-spectrum maximum for wells 6.5 and 7 nm wide is near 6 meV which corresponds to interband optical transitions. The emission is explained by state depletion in the valence band and conduction band filling due to Zener tunneling, which is confirmed by power-law current–voltage characteristics.

  16. Effects of the c-Si/a-SiO2 interfacial atomic structure on its band alignment: an ab initio study.

    Science.gov (United States)

    Zheng, Fan; Pham, Hieu H; Wang, Lin-Wang

    2017-12-13

    The crystalline-Si/amorphous-SiO 2 (c-Si/a-SiO 2 ) interface is an important system used in many applications, ranging from transistors to solar cells. The transition region of the c-Si/a-SiO 2 interface plays a critical role in determining the band alignment between the two regions. However, the question of how this interface band offset is affected by the transition region thickness and its local atomic arrangement is yet to be fully investigated. Here, by controlling the parameters of the classical Monte Carlo bond switching algorithm, we have generated the atomic structures of the interfaces with various thicknesses, as well as containing Si at different oxidation states. A hybrid functional method, as shown by our calculations to reproduce the GW and experimental results for bulk Si and SiO 2 , was used to calculate the electronic structure of the heterojunction. This allowed us to study the correlation between the interface band characterization and its atomic structures. We found that although the systems with different thicknesses showed quite different atomic structures near the transition region, the calculated band offset tended to be the same, unaffected by the details of the interfacial structure. Our band offset calculation agrees well with the experimental measurements. This robustness of the interfacial electronic structure to its interfacial atomic details could be another reason for the success of the c-Si/a-SiO 2 interface in Si-based electronic applications. Nevertheless, when a reactive force field is used to generate the a-SiO 2 and c-Si/a-SiO 2 interfaces, the band offset significantly deviates from the experimental values by about 1 eV.

  17. Valency and molecular structure

    CERN Document Server

    Cartmell, E

    1977-01-01

    Valency and Molecular Structure, Fourth Edition provides a comprehensive historical background and experimental foundations of theories and methods relating to valency and molecular structures. In this edition, the chapter on Bohr theory has been removed while some sections, such as structures of crystalline solids, have been expanded. Details of structures have also been revised and extended using the best available values for bond lengths and bond angles. Recent developments are mostly noted in the chapter on complex compounds, while a new chapter has been added to serve as an introduction t

  18. [Emotional valence of words in schizophrenia].

    Science.gov (United States)

    Jalenques, I; Enjolras, J; Izaute, M

    2013-06-01

    Emotion recognition is a domain in which deficits have been reported in schizophrenia. A number of emotion classification studies have indicated that emotion processing deficits in schizophrenia are more pronounced for negative affects. Given the difficulty of developing material suitable for the study of these emotional deficits, it would be interesting to examine whether patients suffering from schizophrenia are responsive to positively and negatively charged emotion-related words that could be used within the context of remediation strategies. The emotional perception of words was examined in a clinical experiment involving schizophrenia patients. This emotional perception was expressed by the patients in terms of the valence associated with the words. In the present study, we investigated whether schizophrenia patients would assign the same negative and positive valences to words as healthy individuals. Twenty volunteer, clinically stable, outpatients from the Psychiatric Service of the University Hospital of Clermont-Ferrand were recruited. Diagnoses were based on DSM-IV criteria. Global psychiatric symptoms were assessed using the Positive and Negative Symptoms Scale (PANSS). The patients had to evaluate the emotional valence of a set of 300 words on a 5-point scale ranging from "very unpleasant" to "very pleasant". . The collected results were compared with those obtained by Bonin et al. (2003) [13] from 97 University students. Correlational analyses of the two studies revealed that the emotional valences were highly correlated, i.e. the schizophrenia patients estimated very similar emotional valences. More precisely, it was possible to examine three separate sets of 100 words each (positive words, neutral words and negative words). The positive words that were evaluated were the more positive words from the norms collected by Bonin et al. (2003) [13], and the negative words were the more negative examples taken from these norms. The neutral words

  19. Localized description of valence fluctuations

    International Nuclear Information System (INIS)

    Alascio, B.; Allub, R.; Aligia, A.

    1979-07-01

    The authors set up a model for intermediate valence equivalent to the ''atomic'' limit of the Anderson Hamiltonian. Detailed analysis of this model shows that most of the essential characteristics of valence fluctuators are already present in this crudely simplified Hamiltonian. The spin-spin and the 4f charge-charge correlation functions are studied and it is shown that it is possible to define a spin fluctuation frequency ωsub(s.f.) and a charge fluctuation frequency ωsub(ch.f.).ωsub(s.f.) and ωsub(ch.f.) can differ considerably for some values of the parameters of the model. The magnetic susceptibility and the specific heat are calculated as functions of temperature and it is shown how the results simulate the behaviour found in valence fluctuators. (author)

  20. Digital Colour Printing on the Way to Offset Quality

    Directory of Open Access Journals (Sweden)

    Andrew Tribute

    2004-12-01

    Full Text Available Digital production colour printing is now more than ten years old. The first implementations of this technology from Indigo and Xeikon started the market but they suffered problems with reliability,quality and overall running costs. They produced a very good-looking printed image but it was notcomparable to offset. Quality problems were that tints often were streaky or banded, flat tints did notreproduce well, and the overall image had a somewhat harsh reflective look.Ongoing developments of digital colour printing mainly from Xerox and Canon developed the marketand improved the economics of the process. Certain elements of the quality also improved. Indigoand Xeikon also showed significant quality improvements and better economics. The improvedquality came closer to the look of offset, but in most cases was still obviously printed digitally.New developments are happening in what is termed "Digital Colour Lite." This is a range of new slower presses coming from Japan which run at around 30 pages/minute and cost well under 50.000 Euro. A few of these are getting almost offset quality through the use of new chemical toners that significantly improve printing quality.At the same time as the quality of digital colour printing has improved, so have the cost economics of running the presses. Potential buyers of presses will have to understand the different business models for running these presses. These are the "click" models from most suppliers, or the pay by usage model as offered by Heidelberg with the NexPress.

  1. Lunar Noise-Temperature Increase Measurements at S-Band, X-Band, and Ka-Band Using a 34-Meter-Diameter Beam-Waveguide Antenna

    Science.gov (United States)

    Morabito, D. D.

    2006-08-01

    The Moon radiates energy at infrared and microwave wavelengths, in addition to reflecting sunlight at optical wavelengths. As a result, an antenna pointed at or near the Moon will cause an increase in receiver noise temperature that needs to be accounted for in telemetry, radio science, or ranging link budgets. The Deep Space Network may be required to use its antennas in future lunar robotic or human missions, and thus it is important to understand the nature of this temperature increase as a function of observing frequency, lunar phase, and angular offset of the antenna beam from the center of the lunar disk. This article quantifies such a set of measurements acquired at DSS 13, a 34-m-diameter research and development beam-waveguide antenna located at Goldstone, California, at three different telecommunication frequencies, S-band (2.3 GHz), X-band (8.4 GHz), and Ka-band (32 GHz), over a wide range of lunar phase, for both disk-centered and limb-centered positions of the antenna beam.

  2. Low Offset AC Correlator.

    Science.gov (United States)

    This patent describes a low offset AC correlator avoids DC offset and low frequency noise by frequency operating the correlation signal so that low...noise, low level AC amplification can be substituted for DC amplification. Subsequently, the high level AC signal is demodulated to a DC level. (Author)

  3. In-clustering induced anomalousbehavior of band gap in InAlN and InGaN

    DEFF Research Database (Denmark)

    Gorczyca, I.; Suski, T.; Christensen, Niels Egede

    2010-01-01

    Electronic band structure calculations of In containing ternary nitride alloys are presented showing a strong modification of the band gap, EG and its pressure coefficient, dEG/dp, as a function of In-content. Two different arrangements of In atoms are considered: uniform and clustered. It is shown...... that Indium clustering is the additional, large factor leading to the unusual bowings of the band gaps and their pressure coefficients. The theoretical results are compared with experimental data on variations of EG with In content. In the analysis of observed phenomena we point out the particular role...... of the uppermost valence band....

  4. 5 CFR 179.307 - Administrative offset.

    Science.gov (United States)

    2010-01-01

    ... 5 Administrative Personnel 1 2010-01-01 2010-01-01 false Administrative offset. 179.307 Section 179.307 Administrative Personnel OFFICE OF PERSONNEL MANAGEMENT CIVIL SERVICE REGULATIONS CLAIMS COLLECTION STANDARDS Administrative Offset § 179.307 Administrative offset. (a) If the debtor does not...

  5. Electronic structure and optical properties of Cs2HgI4: Experimental study and band-structure DFT calculations

    Science.gov (United States)

    Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Shkumat, P. N.; Myronchuk, G. L.; Khvyshchun, M.; Fedorchuk, A. O.; Parasyuk, O. V.; Khyzhun, O. Y.

    2015-04-01

    High-quality single crystal of cesium mercury tetraiodide, Cs2HgI4, has been synthesized by the vertical Bridgman-Stockbarger method and its crystal structure has been refined. In addition, electronic structure and optical properties of Cs2HgI4 have been studied. For the crystal under study, X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces have been measured. The present X-ray photoelectron spectroscopy (XPS) results indicate that the Cs2HgI4 single crystal surface is very sensitive with respect to Ar+ ion-irradiation. In particular, Ar+ bombardment of the single crystal surface alters the elemental stoichiometry of the Cs2HgI4 surface. To elucidate peculiarities of the energy distribution of the electronic states within the valence-band and conduction-band regions of the Cs2HgI4 compound, we have performed first-principles band-structure calculations based on density functional theory (DFT) as incorporated in the WIEN2k package. Total and partial densities of states for Cs2HgI4 have been calculated. The DFT calculations reveal that the I p states make the major contributions in the upper portion of the valence band, while the Hg d, Cs p and I s states are the dominant contributors in its lower portion. Temperature dependence of the light absorption coefficient and specific electrical conductivity has been explored for Cs2HgI4 in the temperature range of 77-300 K. Main optical characteristics of the Cs2HgI4 compound have been elucidated by the first-principles calculations.

  6. A study of the valence shell spectroscopic and thermodynamic properties of trifluoronitrosomethane cations

    International Nuclear Information System (INIS)

    Graham, D.M.; Powis, I.; Underwood, J.G.; Shaw, D.A.; Holland, D.M.P.

    2012-01-01

    Highlights: ► Fragmentation processes in CF 3 NO have been studied using mass spectrometry. ► Singly charged atomic fragments have been observed. ► Experimental appearance energies have been compared to thermochemical estimates. ► Hartree Fock transition energies and oscillator strengths have been calculated. - Abstract: A time-of-flight mass spectrometry study has been carried out to investigate the fragmentation processes occurring in trifluoronitrosomethane (CF 3 NO) as a result of valence shell photoionisation. Synchrotron radiation has been used to record spectra in the photon energy range ∼10–42 eV, and appearance energies have been determined for 10 fragment ions. At high excitation energies, singly charged atomic fragments have been observed. For the main dissociation channels, leading to the formation of NO + , CF 2 + or CF 3 + , the experimental appearance energies have been compared with thermochemical estimates, and a satisfactory agreement has been found. Structure observed in the total ion yield curve has been interpreted with the aid of excited state transition energies and oscillator strengths obtained in a time-dependent Hartree Fock calculation. The theoretical results show that configuration interaction strongly affects many of the valence states. A HeI excited photoelectron spectrum of CF 3 NO has been measured and the orbital ionisation energies have been compared with theoretical values computed using the Outer Valence Green’s Function approach. A large Franck–Condon gap is observed between the 12a′ (n - ) and the 11a ′ state bands, in accord with the calculated vertical ionisation energies of 10.87 and 16.32 eV for the 12a′ (n − ) and the 11a′ (n + ) orbitals, respectively. In the ion yield curve, the corresponding energy range is strongly influenced by autoionising valence states.

  7. Fluorescence properties of valence-controlled Eu2+ and Mn2+ ions in aluminosilicate glasses

    International Nuclear Information System (INIS)

    Van Tuyen, Ho; Nonaka, Takamasa; Yamanaka, Ken-ichi; Chau, Pham Minh; Quy Hai, Nguyen Thi; Quang, Vu Xuan; Nogami, Masayuki

    2017-01-01

    Controlling of valence states of metal ions doped in glasses has attracted considerable interest due to the possibility of looking toward optical applications. In this study, new Na 2 O-Al 2 O 3 -SiO 2 glasses were developed to dope Eu 2+ and Mn 2+ with well controlled valence states by heating in H 2 gas atmosphere, and the changes in the valence state of doped-ions and their fluorescence properties were investigated using visible and infrared optical absorption spectroscopies, X-ray absorption fine structure spectroscopy, and fluorescence spectroscopy. Among Eu 3+ , Mn 3+ and Mn 2+ ions incorporated in the as-prepared glasses, the Eu 3+ and Mn 3+ ions were reduced to Eu 2+ and Mn 2+ ions, respectively, by heating in H 2 gas and OH bonds were concurrently formed. The fluorescence spectra of glasses heated in H 2 exhibited broad emission bands at 450 and 630 nm wavelength, assigned to the Eu 2+ and Mn 2+ , respectively, ions, in which the fluorescence intensity at 450 nm was observed to decrease with increasing Mn 2+ ion content. The increased fluorescence intensities were analyzed as the energy transfer from Eu 2+ to Mn 2+ ions and the energy transfer efficiency was estimated with a concentration of Eu 2+ and Mn 2+ ions.

  8. Energy band dispersion in photoemission spectra of argon clusters

    International Nuclear Information System (INIS)

    Foerstel, Marko; Mucke, Melanie; Arion, Tiberiu; Lischke, Toralf; Barth, Silko; Ulrich, Volker; Ohrwall, Gunnar; Bjoerneholm, Olle; Hergenhahn, Uwe; Bradshaw, Alex M.

    2011-01-01

    Using photoemission we have investigated free argon clusters from a supersonic nozzle expansion in the photon energy range from threshold up to 28 eV. Measurements were performed both at high resolution with a hemispherical electrostatic energy analyser and at lower resolution with a magnetic bottle device. The latter experiments were performed for various mean cluster sizes. In addition to the ∼1.5 eV broad 3p-derived valence band seen in previous work, there is a sharper feature at ∼15 eV binding energy. Surprisingly for non-oriented clusters, this peak shifts smoothly in binding energy over the narrow photon energy range 15.5-17.7 eV, indicating energy band dispersion. The onset of this bulk band-like behaviour could be determined from the cluster size dependence.

  9. Ab initio electronic band structure study of III-VI layered semiconductors

    Science.gov (United States)

    Olguín, Daniel; Rubio-Ponce, Alberto; Cantarero, Andrés

    2013-08-01

    We present a total energy study of the electronic properties of the rhombohedral γ-InSe, hexagonal ɛ-GaSe, and monoclinic GaTe layered compounds. The calculations have been done using the full potential linear augmented plane wave method, including spin-orbit interaction. The calculated valence bands of the three compounds compare well with angle resolved photoemission measurements and a discussion of the small discrepancies found has been given. The present calculations are also compared with recent and previous band structure calculations available in the literature for the three compounds. Finally, in order to improve the calculated band gap value we have used the recently proposed modified Becke-Johnson correction for the exchange-correlation potential.

  10. Band-gap narrowing of TiO2 films induced by N-doping

    International Nuclear Information System (INIS)

    Nakano, Y.; Morikawa, T.; Ohwaki, T.; Taga, Y.

    2006-01-01

    N-doped TiO 2 films were deposited on n + -GaN/Al 2 O 3 substrates by reactive magnetron sputtering and subsequently crystallized by annealing at 550 o C in flowing N 2 gas. The N-doping concentration was ∼8.8%, as determined from X-ray photoelectron spectroscopy measurements. Deep-level optical spectroscopy measurements revealed two characteristic deep levels located at 1.18 and 2.48 eV below the conduction band. The 1.18 eV level is probably attributable to the O vacancy state and can be active as an efficient generation-recombination center. Additionally, the 2.48 eV band is newly introduced by the N-doping and contributes to band-gap narrowing by mixing with the O 2p valence band

  11. Positive valence music restores executive control over sustained attention.

    Science.gov (United States)

    Baldwin, Carryl L; Lewis, Bridget A

    2017-01-01

    Music sometimes improves performance in sustained attention tasks. But the type of music employed in previous investigations has varied considerably, which can account for equivocal results. Progress has been hampered by lack of a systematic database of music varying in key characteristics like tempo and valence. The aims of this study were to establish a database of popular music varying along the dimensions of tempo and valence and to examine the impact of music varying along these dimensions on restoring attentional resources following performance of a sustained attention to response task (SART) vigil. Sixty-nine participants rated popular musical selections that varied in valence and tempo to establish a database of four musical types: fast tempo positive valence, fast tempo negative valence, slow tempo positive valence, and slow tempo negative valence. A second group of 89 participants performed two blocks of the SART task interspersed with either no break or a rest break consisting of 1 of the 4 types of music or silence. Presenting positive valence music (particularly of slow tempo) during an intermission between two successive blocks of the SART significantly decreased miss rates relative to negative valence music or silence. Results support an attentional restoration theory of the impact of music on sustained attention, rather than arousal theory and demonstrate a means of restoring sustained attention. Further, the results establish the validity of a music database that will facilitate further investigations of the impact of music on performance.

  12. 41 CFR 105-56.018 - Salary offset.

    Science.gov (United States)

    2010-07-01

    ... 41 Public Contracts and Property Management 3 2010-07-01 2010-07-01 false Salary offset. 105-56... Administration 56-SALARY OFFSET FOR INDEBTEDNESS OF FEDERAL EMPLOYEES TO THE UNITED STATES Centralized Salary Offset (CSO) Procedures-GSA as Creditor Agency § 105-56.018 Salary offset. When a match occurs and all...

  13. 41 CFR 105-56.028 - Salary offset.

    Science.gov (United States)

    2010-07-01

    ... 41 Public Contracts and Property Management 3 2010-07-01 2010-07-01 false Salary offset. 105-56... Administration 56-SALARY OFFSET FOR INDEBTEDNESS OF FEDERAL EMPLOYEES TO THE UNITED STATES Centralized Salary Offset (CSO) Procedures-GSA as Paying Agency § 105-56.028 Salary offset. When a match occurs and all...

  14. Moessbauer spectroscopic study on valence-detrapping and trapping of mixed-valence trinuclear iron (III, III, II) fluorine-substitute benzoate complexes

    International Nuclear Information System (INIS)

    Sakai, Y.; Onaka, S.; Ogiso, R.; Takayama, T.; Takahashi, M.; Nakamoto, T.

    2012-01-01

    Four mixed-valence trinuclear iron(III, III, II) fluorine-substituted benzoate complexes were synthesized; Fe 3 O(C 6 F 5 COO) 6 (C 5 H 5 N) 3 ·CH 2 Cl 2 (1), Fe 3 O(C 6 F 5 COO) 6 (C 5 H 5 N) 3 (2), Fe 3 O(2H-C 6 F 4 COO) 6 (C 5 H 5 N) 3 (3), and Fe 3 O(4H-C 6 F 4 COO) 6 (C 5 H 5 N) 3 (4). By means of 57 Fe-Moessbauer spectroscopy, valence-detrapping and trapping phenomena have been investigated for the four mixed-valence complexes. The valence state of three iron ions is trapped at lower temperatures while it is fully detrapped at higher temperatures for 1. Valence detrapping is not observed for 2, 3, and 4 even at room temperature, although Moessbauer spectra for 3 and 4 show a complicated temperature dependence. (author)

  15. Magnetic field induced third order susceptibility of third order harmonic generation in a ZnMgSe strained quantum well

    Energy Technology Data Exchange (ETDEWEB)

    Mark, J. Abraham Hudson, E-mail: a.john.peter@gmail.com; Peter, A. John, E-mail: a.john.peter@gmail.com [Dept. of Physics, SSM Institute of Engineering and Technology, Dindigul-624002 (India)

    2014-04-24

    Third order susceptibility of third order harmonic generation is investigated in a Zn{sub 0.1}Mg{sub 0.9}Se/Zn{sub 0.8}Mg{sub 0.2}Se/Zn{sub 0.1}Mg{sub 0.9}Se quantum well in the presence of magnetic field strength. The confinement potential is considered as the addition of energy offsets of the conduction band (or valence band) and the strain-induced potential in our calculations. The material dependent effective mass is followed throughout the computation because it has a high influence on the electron energy levels in low dimensional semiconductor systems.

  16. 34 CFR 31.11 - Offset process.

    Science.gov (United States)

    2010-07-01

    ... 34 Education 1 2010-07-01 2010-07-01 false Offset process. 31.11 Section 31.11 Education Office of the Secretary, Department of Education SALARY OFFSET FOR FEDERAL EMPLOYEES WHO ARE INDEBTED TO THE UNITED STATES UNDER PROGRAMS ADMINISTERED BY THE SECRETARY OF EDUCATION § 31.11 Offset process. (a) The...

  17. Architectural Representation of Valence in the Limbic System

    Science.gov (United States)

    Namburi, Praneeth; Al-Hasani, Ream; Calhoon, Gwendolyn G; Bruchas, Michael R; Tye, Kay M

    2016-01-01

    In order to thrive, animals must be able to recognize aversive and appetitive stimuli within the environment and subsequently initiate appropriate behavioral responses. This assignment of positive or negative valence to a stimulus is a key feature of emotional processing, the neural substrates of which have been a topic of study for several decades. Until recently, the result of this work has been the identification of specific brain regions, such as the basolateral amygdala (BLA) and nucleus accumbens (NAc), as important to valence encoding. The advent of modern tools in neuroscience has allowed further dissection of these regions to identify specific populations of neurons signaling the valence of environmental stimuli. In this review, we focus upon recent work examining the mechanisms of valence encoding, and provide a model for the systematic investigation of valence within anatomically-, genetically-, and functionally defined populations of neurons. PMID:26647973

  18. Attention-dependent sound offset-related brain potentials.

    Science.gov (United States)

    Horváth, János

    2016-05-01

    When performing sensory tasks, knowing the potentially occurring goal-relevant and irrelevant stimulus events allows the establishment of selective attention sets, which result in enhanced sensory processing of goal-relevant events. In the auditory modality, such enhancements are reflected in the increased amplitude of the N1 ERP elicited by the onsets of task-relevant sounds. It has been recently suggested that ERPs to task-relevant sound offsets are similarly enhanced in a tone-focused state in comparison to a distracted one. The goal of the present study was to explore the influence of attention on ERPs elicited by sound offsets. ERPs elicited by tones in a duration-discrimination task were compared to ERPs elicited by the same tones in not-tone-focused attentional setting. Tone offsets elicited a consistent, attention-dependent biphasic (positive-negative--P1-N1) ERP waveform for tone durations ranging from 150 to 450 ms. The evidence, however, did not support the notion that the offset-related ERPs reflected an offset-specific attention set: The offset-related ERPs elicited in a duration-discrimination condition (in which offsets were task relevant) did not significantly differ from those elicited in a pitch-discrimination condition (in which the offsets were task irrelevant). Although an N2 reflecting the processing of offsets in task-related terms contributed to the observed waveform, this contribution was separable from the offset-related P1 and N1. The results demonstrate that when tones are attended, offset-related ERPs may substantially overlap endogenous ERP activity in the postoffset interval irrespective of tone duration, and attention differences may cause ERP differences in such postoffset intervals. © 2016 Society for Psychophysiological Research.

  19. On triangle meshes with valence dominant vertices

    KAUST Repository

    Morvan, Jean-Marie

    2018-02-16

    We study triangulations $\\\\cal T$ defined on a closed disc $X$ satisfying the following condition: In the interior of $X$, the valence of all vertices of $\\\\cal T$ except one of them (the irregular vertex) is $6$. By using a flat singular Riemannian metric adapted to $\\\\cal T$, we prove a uniqueness theorem when the valence of the irregular vertex is not a multiple of $6$. Moreover, for a given integer $k >1$, we exhibit non isomorphic triangulations on $X$ with the same boundary, and with a unique irregular vertex whose valence is $6k$.

  20. On triangle meshes with valence dominant vertices

    KAUST Repository

    Morvan, Jean-Marie

    2018-01-01

    We study triangulations $\\cal T$ defined on a closed disc $X$ satisfying the following condition: In the interior of $X$, the valence of all vertices of $\\cal T$ except one of them (the irregular vertex) is $6$. By using a flat singular Riemannian metric adapted to $\\cal T$, we prove a uniqueness theorem when the valence of the irregular vertex is not a multiple of $6$. Moreover, for a given integer $k >1$, we exhibit non isomorphic triangulations on $X$ with the same boundary, and with a unique irregular vertex whose valence is $6k$.

  1. Temperature-induced band shift in bulk γ-InSe by angle-resolved photoemission spectroscopy

    Science.gov (United States)

    Xu, Huanfeng; Wang, Wei; Zhao, Yafei; Zhang, Xiaoqian; Feng, Yue; Tu, Jian; Gu, Chenyi; Sun, Yizhe; Liu, Chang; Nie, Yuefeng; Edmond Turcu, Ion C.; Xu, Yongbing; He, Liang

    2018-05-01

    Indium selenide (InSe) has recently become popular research topics because of its unique layered crystal structure, direct band gap and high electron mobilities. In this work, we have acquired the electronic structure of bulk γ-InSe at various temperatures using angle-resolved photoemission spectroscopy (ARPES). We have also found that as the temperature decreases, the valence bands of γ-InSe exhibit a monotonic shift to lower binding energies. This band shift is attributed to the change of lattice parameters and has been validated by variable temperature X-ray diffraction measurements and theoretical calculations.

  2. Offsets - An opportunity of Financing

    International Nuclear Information System (INIS)

    PRIN, Coralie

    2008-01-01

    Nuclear Research Reactors sometimes need to implement projects to upgrade, revamp or convert their reactor, acquire new fuel elements, etc. However, as their activities are mainly of noncommercial nature, they sometimes lack of financial resources to implement these projects by themselves. Several solutions exist: loans, governmental budget, subsidies from international organizations (IAEA). Offsets are another source of financing. They also are free of charge for the reactor. The objective of offsets is to Identify, implement and finance projects that: directly create or sustain a local economic activity of high-added value, would not have happened without the Obligor's intervention, and are of crucial importance given the country's political background (favor employment, technology transfers, training and education, research and development, etc.). Companies worldwide are willing to finance local projects to fulfill their Offset Obligation. Local organizations or institutions are willing to invest to increase their activities but lack of financial resources. Offset regulations are an opportunity on both sides and are free for the local organization. The monetary value of an Offset obligation is calculated as a percentage of the main contract price (or as a percentage of the imported part value). That percentage depends on the Country's legislation and on the nature of the main contract (defense or civilian). This value has to be compensated by an equivalent economic value (a Project's cost is different from its value). There is two ways of assessing a value: - Political aspects: The Project is of political importance for the country (development of an export capability, technology and/or know-how transfers) and the project in line with the country's political priorities (employment, research, international presence, etc.). - Economic benefits: the project directly sustains or creates additional activities, turnover, R and D, employment, etc. It benefits directly

  3. Social learning modulates the lateralization of emotional valence.

    Science.gov (United States)

    Shamay-Tsoory, Simone G; Lavidor, Michal; Aharon-Peretz, Judith

    2008-08-01

    Although neuropsychological studies of lateralization of emotion have emphasized valence (positive vs. negative) or type (basic vs. complex) dimensions, the interaction between the two dimensions has yet to be elucidated. The purpose of the current study was to test the hypothesis that recognition of basic emotions is processed preferentially by the right prefrontal cortex (PFC), whereas recognition of complex social emotions is processed preferentially by the left PFC. Experiment 1 assessed the ability of healthy controls and patients with right and left PFC lesions to recognize basic and complex emotions. Experiment 2 modeled the patient's data of Experiment 1 on healthy participants under lateralized displays of the emotional stimuli. Both experiments support the Type as well as the Valence Hypotheses. However, our findings indicate that the Valence Hypothesis holds for basic but less so for complex emotions. It is suggested that, since social learning overrules the basic preference of valence in the hemispheres, the processing of complex emotions in the hemispheres is less affected by valence.

  4. Valence band electronic structure of Nb{sub 2}Pd{sub 1.2}Se{sub 5} and Nb{sub 2}Pd{sub 0.95}S{sub 5} superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Lohani, H. [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400085 (India); Mishra, P. [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Goyal, R.; Awana, V.P.S. [National Physical Laboratory(CSIR), Dr. K. S. Krishnan Road, New Delhi 110012 (India); Sekhar, B.R., E-mail: sekhar@iopb.res.in [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400085 (India)

    2017-03-15

    We present a comparative study of our valence band photoemission results on Nb{sub 2}Pd{sub 1.2}Se{sub 5} and Nb{sub 2}Pd{sub 0.95}S{sub 5} superconductors which are supported by our DFT based electronic structure calculations. We observe that the VB spectra of both the compounds are qualitatively similar, except for some slight differences in the binding energy positions of all the features. This could be due to the unequal electronegativities of Se and S atom. The calculated density of states (DOS) reveals that the VB features are mainly composed of Pd-Se/S hybridized states. The nature of DOS originating from the distinctly coordinated Pd atoms is different. Further, various Pd-4d and Nb-4d states crossing the Fermi level (E{sub f}) signifies the multiband character of these compounds. In addition, we find a temperature dependent pseudogap in Nb{sub 2}Pd{sub 0.95}S{sub 5} which is absent in Nb{sub 2}Pd{sub 1.2}Se{sub 5}.

  5. Modeling and experimental studies of a side band power re-injection locked magnetron

    Science.gov (United States)

    Ye, Wen-Jun; Zhang, Yi; Yuan, Ping; Zhu, Hua-Cheng; Huang, Ka-Ma; Yang, Yang

    2016-12-01

    A side band power re-injection locked (SBPRIL) magnetron is presented in this paper. A tuning stub is placed between the external injection locked (EIL) magnetron and the circulator. Side band power of the EIL magnetron is reflected back to the magnetron. The reflected side band power is reused and pulled back to the central frequency. A phase-locking model is developed from circuit theory to explain the process of reuse of side band power in SBPRIL magnetron. Theoretical analysis proves that the side band power is pulled back to the central frequency of the SBPRIL magnetron, then the amplitude of the RF voltage increases and the phase noise performance is improved. Particle-in-cell (PIC) simulation of a 10-vane continuous wave (CW) magnetron model is presented. Computer simulation predicts that the frequency spectrum’s peak of the SBPRIL magnetron has an increase of 3.25 dB compared with the free running magnetron. The phase noise performance at the side band offset reduces 12.05 dB for the SBPRIL magnetron. Besides, the SBPRIL magnetron experiment is presented. Experimental results show that the spectrum peak rises by 14.29% for SBPRIL magnetron compared with the free running magnetron. The phase noise reduces more than 25 dB at 45-kHz offset compared with the free running magnetron. Project supported by the National Basic Research Program of China (Grant No. 2013CB328902) and the National Natural Science Foundation of China (Grant No. 61501311).

  6. Calculation of Energy Diagram of Asymmetric Graded-Band-Gap Semiconductor Superlattices.

    Science.gov (United States)

    Monastyrskii, Liubomyr S; Sokolovskii, Bogdan S; Alekseichyk, Mariya P

    2017-12-01

    The paper theoretically investigates the peculiarities of energy diagram of asymmetric graded-band-gap superlattices with linear coordinate dependences of band gap and electron affinity. For calculating the energy diagram of asymmetric graded-band-gap superlattices, linearized Poisson's equation has been solved for the two layers forming a period of the superlattice. The obtained coordinate dependences of edges of the conduction and valence bands demonstrate substantial transformation of the shape of the energy diagram at changing the period of the lattice and the ratio of width of the adjacent layers. The most marked changes in the energy diagram take place when the period of lattice is comparable with the Debye screening length. In the case when the lattice period is much smaller that the Debye screening length, the energy diagram has the shape of a sawtooth-like pattern.

  7. Valence nucleons in self-consistent fields

    International Nuclear Information System (INIS)

    Di Toro, M.; Lomnitz-Adler, J.

    1978-01-01

    An iterative approach to determine directly the best Hartree-Fock one-body density rho is extended by expressing rho in terms of a core and a valence part and allowing for general crossings of occupied and unoccupied levels in the valence part. Results are shown for 152 Sm and a microscopic analysis of the core structure of deformed light nuclei is carried out. (author)

  8. Resonant photoelectron spectroscopy of γ-Al{sub 2}O{sub 3}/SrTiO{sub 3} heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Schuetz, Philipp; Pfaff, Florian; Zapf, Michael; Gabel, Judith; Dudy, Lenart; Berner, Goetz; Sing, Michael; Claessen, Ralph [Wuerzburg Univ. (Germany). Physikalisches Inst. and Roentgen Center for Complex Material Systems (RCCM); Chen, Yunzhong; Pryds, Nini [Technical Univ. of Denmark, Risoe (Denmark). Dept. of Energy Conversion and Storage; Rogalev, Victor; Strocov, Vladimir [Paul Scherrer Institut, Villigen (Switzerland). Swiss Light Source; Schlueter, Christoph; Lee, Tien-Lin [Diamond Light Source Ltd., Didcot (United Kingdom)

    2015-07-01

    The spinel/perovskite heterointerface between the band insulators γ-Al{sub 2}O{sub 3} and SrTiO{sub 3} hosts a two-dimensional electron system (2DES) with exceptionally high electron mobility. Soft X-ray resonant photoelectron spectroscopy at the Ti L absorption edge is used to probe the Ti 3d derived interface states. Marked differences in the resonance behavior are found for the SrTiO{sub 3} valence band and the different interface states, which are observed in the band gap of SrTiO{sub 3}. A comparison to X-ray absorption spectra of Ti 3d{sup 0} and Ti 3d{sup 1} systems reveals the presence of different types of electronic states with Ti 3d character, i.e., oxygen vacancy induced, trapped in-gap states and itinerant states contributing to the 2DES. Furthermore, exposure to low doses of oxygen during irradiation allows for the controlled and reversible manipulation of the interfacial electronic structure, i.e., the in-gap state intensity and the valence band offset between SrTiO{sub 3} and γ-Al{sub 2}O{sub 3}.

  9. 41 CFR 105-56.019 - Offset amount.

    Science.gov (United States)

    2010-07-01

    ... Administration 56-SALARY OFFSET FOR INDEBTEDNESS OF FEDERAL EMPLOYEES TO THE UNITED STATES Centralized Salary... referred for offset under this subpart is $100. (b) The amount offset from a salary payment under this... resolved to the satisfaction of GSA. ...

  10. Electronic structure study of wide band gap magnetic semiconductor (La0.6Pr0.4)0.65Ca0.35MnO3 nanocrystals in paramagnetic and ferromagnetic phases

    Science.gov (United States)

    Dwivedi, G. D.; Joshi, Amish G.; Kumar, Shiv; Chou, H.; Yang, K. S.; Jhong, D. J.; Chan, W. L.; Ghosh, A. K.; Chatterjee, Sandip

    2016-04-01

    X-ray circular magnetic dichroism (XMCD), X-ray photoemission spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) techniques were used to study the electronic structure of nanocrystalline (La0.6Pr0.4)0.65Ca0.35MnO3 near Fermi-level. XMCD results indicate that Mn3+ and Mn4+ spins are aligned parallel to each other at 20 K. The low M-H hysteresis curve measured at 5 K confirms ferromagnetic ordering in the (La0.6Pr0.4)0.65Ca0.35MnO3 system. The low temperature valence band XPS indicates that coupling between Mn3d and O2p is enhanced and the electronic states near Fermi-level have been suppressed below TC. The valence band UPS also confirms the suppression of electronic states near Fermi-level below Curie temperature. UPS near Fermi-edge shows that the electronic states are almost absent below 0.5 eV (at 300 K) and 1 eV (at 115 K). This absence clearly demonstrates the existence of a wide band-gap in the system since, for hole-doped semiconductors, the Fermi-level resides just above the valence band maximum.

  11. ENDOR with band-selective shaped inversion pulses

    Science.gov (United States)

    Tait, Claudia E.; Stoll, Stefan

    2017-04-01

    Electron Nuclear DOuble Resonance (ENDOR) is based on the measurement of nuclear transition frequencies through detection of changes in the polarization of electron transitions. In Davies ENDOR, the initial polarization is generated by a selective microwave inversion pulse. The rectangular inversion pulses typically used are characterized by a relatively low selectivity, with full inversion achieved only for a limited number of spin packets with small resonance offsets. With the introduction of pulse shaping to EPR, the rectangular inversion pulses can be replaced with shaped pulses with increased selectivity. Band-selective inversion pulses are characterized by almost rectangular inversion profiles, leading to full inversion for spin packets with resonance offsets within the pulse excitation bandwidth and leaving spin packets outside the excitation bandwidth largely unaffected. Here, we explore the consequences of using different band-selective amplitude-modulated pulses designed for NMR as the inversion pulse in ENDOR. We find an increased sensitivity for small hyperfine couplings compared to rectangular pulses of the same bandwidth. In echo-detected Davies-type ENDOR, finite Fourier series inversion pulses combine the advantages of increased absolute ENDOR sensitivity of short rectangular inversion pulses and increased sensitivity for small hyperfine couplings of long rectangular inversion pulses. The use of pulses with an almost rectangular frequency-domain profile also allows for increased control of the hyperfine contrast selectivity. At X-band, acquisition of echo transients as a function of radiofrequency and appropriate selection of integration windows during data processing allows efficient separation of contributions from weakly and strongly coupled nuclei in overlapping ENDOR spectra within a single experiment.

  12. Interfacial, Electrical, and Band Alignment Characteristics of HfO2/Ge Stacks with In Situ-Formed SiO2 Interlayer by Plasma-Enhanced Atomic Layer Deposition

    Science.gov (United States)

    Cao, Yan-Qiang; Wu, Bing; Wu, Di; Li, Ai-Dong

    2017-05-01

    In situ-formed SiO2 was introduced into HfO2 gate dielectrics on Ge substrate as interlayer by plasma-enhanced atomic layer deposition (PEALD). The interfacial, electrical, and band alignment characteristics of the HfO2/SiO2 high-k gate dielectric stacks on Ge have been well investigated. It has been demonstrated that Si-O-Ge interlayer is formed on Ge surface during the in situ PEALD SiO2 deposition process. This interlayer shows fantastic thermal stability during annealing without obvious Hf-silicates formation. In addition, it can also suppress the GeO2 degradation. The electrical measurements show that capacitance equivalent thickness of 1.53 nm and a leakage current density of 2.1 × 10-3 A/cm2 at gate bias of Vfb + 1 V was obtained for the annealed sample. The conduction (valence) band offsets at the HfO2/SiO2/Ge interface with and without PDA are found to be 2.24 (2.69) and 2.48 (2.45) eV, respectively. These results indicate that in situ PEALD SiO2 may be a promising interfacial control layer for the realization of high-quality Ge-based transistor devices. Moreover, it can be demonstrated that PEALD is a much more powerful technology for ultrathin interfacial control layer deposition than MOCVD.

  13. Contact Selectivity Engineering in a 2 μm Thick Ultrathin c-Si Solar Cell Using Transition-Metal Oxides Achieving an Efficiency of 10.8.

    Science.gov (United States)

    Xue, Muyu; Islam, Raisul; Meng, Andrew C; Lyu, Zheng; Lu, Ching-Ying; Tae, Christian; Braun, Michael R; Zang, Kai; McIntyre, Paul C; Kamins, Theodore I; Saraswat, Krishna C; Harris, James S

    2017-12-06

    In this paper, the integration of metal oxides as carrier-selective contacts for ultrathin crystalline silicon (c-Si) solar cells is demonstrated which results in an ∼13% relative improvement in efficiency. The improvement in efficiency originates from the suppression of the contact recombination current due to the band offset asymmetry of these oxides with Si. First, an ultrathin c-Si solar cell having a total thickness of 2 μm is shown to have >10% efficiency without any light-trapping scheme. This is achieved by the integration of nickel oxide (NiO x ) as a hole-selective contact interlayer material, which has a low valence band offset and high conduction band offset with Si. Second, we show a champion cell efficiency of 10.8% with the additional integration of titanium oxide (TiO x ), a well-known material for an electron-selective contact interlayer. Key parameters including V oc and J sc also show different degrees of enhancement if single (NiO x only) or double (both NiO x and TiO x ) carrier-selective contacts are integrated. The fabrication process for TiO x and NiO x layer integration is scalable and shows good compatibility with the device.

  14. Band structure engineering for ultracold quantum gases in optical lattices

    International Nuclear Information System (INIS)

    Weinberg, Malte

    2014-01-01

    the same system maps onto a quantum spin-1/2 XY model. Owing to the quantum nature of the pseudospins, geometrical frustration leads to a highly degenerate ground state which can result in exotic valence bond spin-liquid phases. First signatures of an order-by-disorder effect emerge in this regime. A complementary approach to the manipulation of the band structure is investigated in a honeycomb potential. By rotating the quantization field of the system, the statedependent energy offset between the twofold atomic basis of the hexagonal Bravais lattice can be adjusted. This purposeful breaking of inversion symmetry enables the continuous opening of an energy gap at the Dirac points of the honeycomb band structure. In addition, a striking influence of the band gap onto the lifetimes for atoms in the first excited energy band is observed. In the last part of the thesis, both experimental manipulation techniques are discussed with respect to future applications for ultracold quantum gases in non-cubic optical lattices.

  15. 41 CFR 105-56.029 - Offset amount.

    Science.gov (United States)

    2010-07-01

    ... Administration 56-SALARY OFFSET FOR INDEBTEDNESS OF FEDERAL EMPLOYEES TO THE UNITED STATES Centralized Salary... salary offset under this subpart is $100. (b) The amount offset from a salary payment under this subpart... otherwise resolved to the satisfaction of the creditor agency. ...

  16. Theory for the mixed-valence state

    International Nuclear Information System (INIS)

    Varma, C.M.

    1979-01-01

    A theory is presented which explains why mixed-valence compounds behave as two component Fermi liquids, and why TmSe orders magnetically while the other known mixed-valence compounds do not. The variation of Tsub(N) and the field Hsub(T) to obtain ferromagnetic alignment with changing Tm 2+ /Tm 3+ ratio is quantitatively explained. For Tm 2+ concentration > = 0.3, TmSe is predicted to order ferromagnetically

  17. 5 CFR 1639.27 - Procedures for salary offset.

    Science.gov (United States)

    2010-01-01

    ... 5 Administrative Personnel 3 2010-01-01 2010-01-01 false Procedures for salary offset. 1639.27... Salary Offset § 1639.27 Procedures for salary offset. (a) The Board will coordinate salary deductions... pay and will implement the salary offset. (c) Deductions will begin within three official pay periods...

  18. 22 CFR 309.17 - Procedures for salary offset.

    Science.gov (United States)

    2010-04-01

    ... 22 Foreign Relations 2 2010-04-01 2010-04-01 true Procedures for salary offset. 309.17 Section 309.17 Foreign Relations PEACE CORPS DEBT COLLECTION Salary Offset § 309.17 Procedures for salary offset. Unless otherwise provided by statute or contract, the following procedures apply to salary offset: (a...

  19. 7 CFR 3.46 - Offset against tax refunds.

    Science.gov (United States)

    2010-01-01

    ... 7 Agriculture 1 2010-01-01 2010-01-01 false Offset against tax refunds. 3.46 Section 3.46 Agriculture Office of the Secretary of Agriculture DEBT MANAGEMENT Administrative Offset § 3.46 Offset against tax refunds. USDA will take action to effect administrative offset against tax refunds due to debtors...

  20. f-band narrowing in uranium intermetallics

    International Nuclear Information System (INIS)

    Dunlap, B.D.; Litterst, F.J.; Malik, S.K.; Kierstead, H.A.; Crabtree, G.W.; Kwok, W.; Lam, D.J.; Mitchell, A.W.

    1987-01-01

    Although the discovery of heavy fermion behavior in uranium compounds has attracted a great deal of attention, relatively little work has been done which is sufficiently systematic to allow an assessment of the relationship of such behavior to more common phenomena, such as mixed valence, narrow-band effects, etc. In this paper we report bulk property measurements for a number of alloys which form a part of such a systematic study. The approach has been to take relatively simple and well-understood materials and alter their behavior by alloying to produce heavy fermion or Kondo behavior in a controlled way

  1. Band structure engineering and vacancy induced metallicity at the GaAs-AlAs interface

    KAUST Repository

    Upadhyay Kahaly, M.

    2011-09-20

    We study the epitaxial GaAs-AlAs interface of wide gap materials by full-potential density functional theory. AlAsthin films on a GaAs substrate and GaAsthin films on an AlAs substrate show different trends for the electronic band gap with increasing film thickness. In both cases, we find an insulating state at the interface and a negligible charge transfer even after relaxation. Differences in the valence and conduction band edges suggest that the energy band discontinuities depend on the growth sequence. Introduction of As vacancies near the interface induces metallicity, which opens great potential for GaAs-AlAs heterostructures in modern electronics.

  2. 5 CFR 179.211 - Notice of salary offset.

    Science.gov (United States)

    2010-01-01

    ... 5 Administrative Personnel 1 2010-01-01 2010-01-01 false Notice of salary offset. 179.211 Section... COLLECTION STANDARDS Salary Offset § 179.211 Notice of salary offset. (a) Upon receipt of proper... certification as the debtor, a written notice of salary offset. Such notice shall, at a minimum: (1) State that...

  3. High-order harmonic generation from a two-dimensional band structure

    Science.gov (United States)

    Jin, Jian-Zhao; Xiao, Xiang-Ru; Liang, Hao; Wang, Mu-Xue; Chen, Si-Ge; Gong, Qihuang; Peng, Liang-You

    2018-04-01

    In the past few years, harmonic generation in solids has attracted tremendous attention. Recently, some experiments of two-dimensional (2D) monolayer or few-layer materials have been carried out. These studies demonstrated that harmonic generation in the 2D case shows a strong dependence on the laser's orientation and ellipticity, which calls for a quantitative theoretical interpretation. In this work, we carry out a systematic study on the harmonic generation from a 2D band structure based on a numerical solution to the time-dependent Schrödinger equation. By comparing with the 1D case, we find that the generation dynamics can have a significant difference due to the existence of many crossing points in the 2D band structure. In particular, the higher conduction bands can be excited step by step via these crossing points and the total contribution of the harmonic is given by the mixing of transitions between different clusters of conduction bands to the valence band. We also present the orientation dependence of the harmonic yield on the laser polarization direction.

  4. Probing Transient Valence Orbital Changes with Picosecond Valence-to-Core X-ray Emission Spectroscopy

    DEFF Research Database (Denmark)

    March, Anne Marie; Assefa, Tadesse A.; Boemer, Christina

    2017-01-01

    We probe the dynamics of valence electrons in photoexcited [Fe(terpy)2]2+ in solution to gain deeper insight into the Fe ligand bond changes. We use hard X-ray emission spectroscopy (XES), which combines element specificity and high penetration with sensitivity to orbital structure, making...... valence orbitals to the nascent core-hole. Vtc-XES offers particular insight into the molecular orbitals directly involved in the light-driven dynamics; a change in the metal ligand orbital overlap results in an intensity reduction and a blue energy shift in agreement with our theoretical calculations...... and more subtle features at the highest energies reflect changes in the frontier orbital populations....

  5. A direct-conversion WLAN transceiver baseband with DC offset compensation and carrier leakage reduction

    Energy Technology Data Exchange (ETDEWEB)

    Yuan Fang; Yan Jun; Ma Heping; Shi Yin [Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Foster, Dai Fa, E-mail: fyuan@sci-inc.com.c [Department of Electrical and Computer Engineering, Auburn University, Auburn, AL 36849-5201 (United States)

    2010-10-15

    A dual-band direct-conversion WLAN transceiver baseband compliant with the IEEE 802.11a/b/g standards is described. Several critical techniques for receiver DC offset compensation and transmitter carrier leakage rejection calibration are presented that enable the direct-conversion architecture to meet all WLAN specifications. The receiver baseband VGA provides 62 dB gain range with steps of 2 dB and a DC offset cancellation circuit is introduced to remove the offset from layout and self-mixing. The calibration loop achieves constant high-pass pole when gain changes; and a fast response time by programming the pole to 1 MHz during preamble and to 30 kHz during receiving data. The transmitter baseband employs an auto-calibration loop with on-chip AD and DA to suppress the carrier leakage, and AD can be powered down after calibration to save power consumption. The chip consumes 17.52 mA for RX baseband VGA and DCOC, and 8.3 mA for TX carrier leakage calibration (5.88 mA after calibration) from 2.85 V supply. Implemented in a 0.35 {mu}m SiGe technology, they occupy 0.68 mm{sup 2} and 0.18 mm{sup 2} die size respectively. (semiconductor integrated circuits)

  6. Importance-truncated shell model for multi-shell valence spaces

    Energy Technology Data Exchange (ETDEWEB)

    Stumpf, Christina; Vobig, Klaus; Roth, Robert [Institut fuer Kernphysik, TU Darmstadt (Germany)

    2016-07-01

    The valence-space shell model is one of the work horses in nuclear structure theory. In traditional applications, shell-model calculations are carried out using effective interactions constructed in a phenomenological framework for rather small valence spaces, typically spanned by one major shell. We improve on this traditional approach addressing two main aspects. First, we use new effective interactions derived in an ab initio approach and, thus, establish a connection to the underlying nuclear interaction providing access to single- and multi-shell valence spaces. Second, we extend the shell model to larger valence spaces by applying an importance-truncation scheme based on a perturbative importance measure. In this way, we reduce the model space to the relevant basis states for the description of a few target eigenstates and solve the eigenvalue problem in this physics-driven truncated model space. In particular multi-shell valence spaces are not tractable otherwise. We combine the importance-truncated shell model with refined extrapolation schemes to approximately recover the exact result. We present first results obtained in the importance-truncated shell model with the newly derived ab initio effective interactions for multi-shell valence spaces, e.g., the sdpf shell.

  7. The performance of DC restoration function for MODIS thermal emissive bands

    Science.gov (United States)

    Wang, Zhipeng; Xiong, Xiaoxiong Jack; Shrestha, Ashish

    2017-09-01

    The DC restore (DCR) process of MODIS instrument maintains the output of a detector at focal plane assembly (FPA) within the dynamic range of subsequent analog-to-digital converter, by adding a specific offset voltage to the output. The DCR offset value is adjusted per scan, based on the comparison of the detector response in digital number (DN) collected from the blackbody (BB) view with target DN saved as an on-board look-up table. In this work, the MODIS DCR mechanism is revisited, with the trends of DCR offset being provided for thermal emissive bands (TEB). Noticeable changes have been occasionally found which coincide with significant detector gain change due to various instrumental events such as safe-mode anomaly or FPA temperature fluctuation. In general, MODIS DCR functionality has been effective and the change of DCR offset has no impact to the quality of MODIS data. One exception is the Earth view (EV) data saturation of Aqua MODIS LWIR bands 33, 35 ad 36 during BB warm-up cool-down (WUCD) cycle which has been observed since 2008. The BB view of their detectors saturate when the BB temperature is above certain threshold so the DCR cannot work as designed. Therefore, the dark signal DN fluctuates with the cold FPA (CFPA) temperature and saturate for a few hours per WUCD cycle, which also saturate the EV data sector within the scan. The CFPA temperature fluctuation peaked in 2012 and has been reduced in recent years and the saturation phenomenon has been easing accordingly. This study demonstrates the importance of DCR to data generation.

  8. 12 CFR 1408.39 - Procedures for salary offset.

    Science.gov (United States)

    2010-01-01

    ... 12 Banks and Banking 7 2010-01-01 2010-01-01 false Procedures for salary offset. 1408.39 Section... STATES Offset Against Salary § 1408.39 Procedures for salary offset. (a) The Chairman, or designee of the... periods following the date of mailing or delivery of the Notice of Intent to Collect by Salary Offset. (c...

  9. 12 CFR 608.839 - Procedures for salary offset.

    Science.gov (United States)

    2010-01-01

    ... 12 Banks and Banking 6 2010-01-01 2010-01-01 false Procedures for salary offset. 608.839 Section... OWED THE UNITED STATES Offset Against Salary § 608.839 Procedures for salary offset. (a) The Chairman... Intent to Collect by Salary Offset. (c)(1) If the amount of the debt is equal to or is less than 15...

  10. Universality class of non-Fermi liquid behaviour in mixed valence systems

    International Nuclear Information System (INIS)

    Zhang Guangming; Su Zhaobin; Lu Yu

    1995-11-01

    A generalized Anderson single-impurity model with off-site Coulomb interactions is derived from the extended three-band Hubbard model, originally proposed to describe the physics of the copper-oxides. Using the abelian bosonization technique and canonical transformations, an effective Hamiltonian is derived in the strong coupling limit, which is essentially analogous to the Toulouse limit of the ordinary Kondo problem. In this limit, the effective Hamiltonian can be exactly solved, with a mixed valence quantum critical point separating two different Fermi liquid phases, i.e. the Kondo phase and the empty orbital phase. In the mixed valence quantum critical regime, the local moment is only partially quenched and X-ray edge singularities are generated. Around the quantum critical point, a new type of non-Fermi liquid behaviour is predicted with an extra specific heat C imp ∼ T 1/4 and a singular spin-susceptibility χ imp ∼ T -3/4 . At the same time, the effective Hamiltonian under single occupancy is transformed into a resonant-level model, from which the correct Kondo physical properties (specific heat, spin susceptibility, and an enhanced Wilson ratio) are easily rederived. Finally, a brief discussion is given to relate these theoretical results to observations in U Pd x Cu 5-x (x=1, 1.5) alloys, which show single-impurity critical behaviour consistent with our predictions. (author). 30 refs

  11. Universality class of non-Fermi-liquid behavior in mixed-valence systems

    Science.gov (United States)

    Zhang, Guang-Ming; Su, Zhao-Bin; Yu, Lu

    1996-01-01

    A generalized Anderson single-impurity model with off-site Coulomb interactions is derived from the extended three-band Hubbard model, originally proposed to describe the physics of the copper oxides. Using the Abelian bosonization technique and canonical transformations, an effective Hamiltonian is derived in the strong-coupling limit, which is essentially analogous to the Toulouse limit of the ordinary Kondo problem. In this limit, the effective Hamiltonian can be exactly solved, with a mixed-valence quantum critical point separating two different Fermi-liquid phases, i.e., the Kondo phase and the empty orbital phase. In the mixed-valence quantum critical regime, the local moment is only partially quenched and x-ray edge singularities are generated. Around the quantum critical point, a type of non-Fermi-liquid behavior is predicted with an extra specific heat Cimp~T1/4 and a singular spin susceptibility χimp~T-3/4. At the same time, the effective Hamiltonian under single occupancy is transformed into a resonant-level model, from which the correct Kondo physical properties (specific heat, spin susceptibility, and an enhanced Wilson ratio) are easily rederived. Finally, a brief discussion is given to relate these theoretical results to observations in UPdxCu5-x (x=1,1.5) alloys, which show single-impurity critical behavior consistent with our predictions.

  12. 13 CFR 120.1722 - SBA's offset rights.

    Science.gov (United States)

    2010-01-01

    ... 13 Business Credit and Assistance 1 2010-01-01 2010-01-01 false SBA's offset rights. 120.1722... of SBA Secondary Market Guarantee Program for First Lien Position 504 Loan Pools § 120.1722 SBA's offset rights. SBA shall have the right to offset any amount owed by Lender to SBA, including, without...

  13. Valence-Dependent Belief Updating: Computational Validation

    Directory of Open Access Journals (Sweden)

    Bojana Kuzmanovic

    2017-06-01

    Full Text Available People tend to update beliefs about their future outcomes in a valence-dependent way: they are likely to incorporate good news and to neglect bad news. However, belief formation is a complex process which depends not only on motivational factors such as the desire for favorable conclusions, but also on multiple cognitive variables such as prior beliefs, knowledge about personal vulnerabilities and resources, and the size of the probabilities and estimation errors. Thus, we applied computational modeling in order to test for valence-induced biases in updating while formally controlling for relevant cognitive factors. We compared biased and unbiased Bayesian models of belief updating, and specified alternative models based on reinforcement learning. The experiment consisted of 80 trials with 80 different adverse future life events. In each trial, participants estimated the base rate of one of these events and estimated their own risk of experiencing the event before and after being confronted with the actual base rate. Belief updates corresponded to the difference between the two self-risk estimates. Valence-dependent updating was assessed by comparing trials with good news (better-than-expected base rates with trials with bad news (worse-than-expected base rates. After receiving bad relative to good news, participants' updates were smaller and deviated more strongly from rational Bayesian predictions, indicating a valence-induced bias. Model comparison revealed that the biased (i.e., optimistic Bayesian model of belief updating better accounted for data than the unbiased (i.e., rational Bayesian model, confirming that the valence of the new information influenced the amount of updating. Moreover, alternative computational modeling based on reinforcement learning demonstrated higher learning rates for good than for bad news, as well as a moderating role of personal knowledge. Finally, in this specific experimental context, the approach based on

  14. Emotion and language: Valence and arousal affect word recognition

    Science.gov (United States)

    Brysbaert, Marc; Warriner, Amy Beth

    2014-01-01

    Emotion influences most aspects of cognition and behavior, but emotional factors are conspicuously absent from current models of word recognition. The influence of emotion on word recognition has mostly been reported in prior studies on the automatic vigilance for negative stimuli, but the precise nature of this relationship is unclear. Various models of automatic vigilance have claimed that the effect of valence on response times is categorical, an inverted-U, or interactive with arousal. The present study used a sample of 12,658 words, and included many lexical and semantic control factors, to determine the precise nature of the effects of arousal and valence on word recognition. Converging empirical patterns observed in word-level and trial-level data from lexical decision and naming indicate that valence and arousal exert independent monotonic effects: Negative words are recognized more slowly than positive words, and arousing words are recognized more slowly than calming words. Valence explained about 2% of the variance in word recognition latencies, whereas the effect of arousal was smaller. Valence and arousal do not interact, but both interact with word frequency, such that valence and arousal exert larger effects among low-frequency words than among high-frequency words. These results necessitate a new model of affective word processing whereby the degree of negativity monotonically and independently predicts the speed of responding. This research also demonstrates that incorporating emotional factors, especially valence, improves the performance of models of word recognition. PMID:24490848

  15. Utilization of curve offsets in additive manufacturing

    Science.gov (United States)

    Haseltalab, Vahid; Yaman, Ulas; Dolen, Melik

    2018-05-01

    Curve offsets are utilized in different fields of engineering and science. Additive manufacturing, which lately becomes an explicit requirement in manufacturing industry, utilizes curve offsets widely. One of the necessities of offsetting is for scaling which is required if there is shrinkage after the fabrication or if the surface quality of the resulting part is unacceptable. Therefore, some post-processing is indispensable. But the major application of curve offsets in additive manufacturing processes is for generating head trajectories. In a point-wise AM process, a correct tool-path in each layer can reduce lots of costs and increase the surface quality of the fabricated parts. In this study, different curve offset generation algorithms are analyzed to show their capabilities and disadvantages through some test cases and improvements on their drawbacks are suggested.

  16. 10 CFR 1015.215 - Federal salary offset.

    Science.gov (United States)

    2010-01-01

    ... 10 Energy 4 2010-01-01 2010-01-01 false Federal salary offset. 1015.215 Section 1015.215 Energy... Administrative Collection of Claims § 1015.215 Federal salary offset. (a) DOE may authorize Treasury to offset a Federal salary to satisfy delinquent debt in accordance with 5 U.S.C. 5514, Installment Deduction for...

  17. Band formation in xenon-argon alloys studied by photoelectron spectroscopy

    International Nuclear Information System (INIS)

    Nuernberger, R.; Himpsel, F.J.; Schwentner, N.; Koch, E.E.

    1977-01-01

    Photoelectron energy distribution curves for Xenon-Argon alloys for concentrations ranging from 0-100% have been measured by excitation with synchrotron radiation at hupsilon = 13.8 eV, 16.5 eV and 18.0 eV. With increasing Xe concentration the gradual formation of Xe valence bands starting from the atomic Xe 5p 1 / 2 and Xe 5p 3 / 2 states is observed. Similarly with Ar the 3p states are broadened with increasing Ar concentration. Rather high concentrations of Xe or Ar are necessary in order to reach the fully developed Xe or Ar bands respectively. The results are discussed in terms of a concentration dependent tightbinding bandstructure. (orig.) [de

  18. Optical properties of chalcopyrite-type intermediate transition metal band materials from first principles

    International Nuclear Information System (INIS)

    Aguilera, I.; Palacios, P.; Wahnon, P.

    2008-01-01

    The optical properties of a novel potential high-efficiency photovoltaic material have been studied. This material is based on a chalcopyrite-type semiconductor (CuGaS 2 ) with some Ga atom substituted by Ti and is characterized by the formation of an isolated transition-metal band between the valence band and the conduction band. We present a study in which ab-initio density functional theory calculations within the generalized gradient approximation are carried out to determine the optical reflectivity and absorption coefficient of the materials of interest. Calculations for the host semiconductor are in good agreement with experimental results within the limitations of the approach. We find, as desired, that because of the intermediate band, the new Ti-substituted material would be able to absorb photons of energy lower than the band-gap of the host chalcopyrite. We also analyze the partial contributions to the main peaks of its spectrum

  19. Valenced cues and contexts have different effects on event-based prospective memory.

    Science.gov (United States)

    Graf, Peter; Yu, Martin

    2015-01-01

    This study examined the separate influence and joint influences on event-based prospective memory task performance due to the valence of cues and the valence of contexts. We manipulated the valence of cues and contexts with pictures from the International Affective Picture System. The participants, undergraduate students, showed higher performance when neutral compared to valenced pictures were used for cueing prospective memory. In addition, neutral pictures were more effective as cues when they occurred in a valenced context than in the context of neutral pictures, but the effectiveness of valenced cues did not vary across contexts that differed in valence. The finding of an interaction between cue and context valence indicates that their respective influence on event-based prospective memory task performance cannot be understood in isolation from each other. Our findings are not consistent with by the prevailing view which holds that the scope of attention is broadened and narrowed, respectively, by positively and negatively valenced stimuli. Instead, our findings are more supportive of the recent proposal that the scope of attention is determined by the motivational intensity associated with valenced stimuli. Consistent with this proposal, we speculate that the motivational intensity associated with different retrieval cues determines the scope of attention, that contexts with different valence values determine participants' task engagement, and that prospective memory task performance is determined jointly by attention scope and task engagement.

  20. Valenced cues and contexts have different effects on event-based prospective memory.

    Directory of Open Access Journals (Sweden)

    Peter Graf

    Full Text Available This study examined the separate influence and joint influences on event-based prospective memory task performance due to the valence of cues and the valence of contexts. We manipulated the valence of cues and contexts with pictures from the International Affective Picture System. The participants, undergraduate students, showed higher performance when neutral compared to valenced pictures were used for cueing prospective memory. In addition, neutral pictures were more effective as cues when they occurred in a valenced context than in the context of neutral pictures, but the effectiveness of valenced cues did not vary across contexts that differed in valence. The finding of an interaction between cue and context valence indicates that their respective influence on event-based prospective memory task performance cannot be understood in isolation from each other. Our findings are not consistent with by the prevailing view which holds that the scope of attention is broadened and narrowed, respectively, by positively and negatively valenced stimuli. Instead, our findings are more supportive of the recent proposal that the scope of attention is determined by the motivational intensity associated with valenced stimuli. Consistent with this proposal, we speculate that the motivational intensity associated with different retrieval cues determines the scope of attention, that contexts with different valence values determine participants' task engagement, and that prospective memory task performance is determined jointly by attention scope and task engagement.

  1. Design of medium band gap Ag-Bi-Nb-O and Ag-Bi-Ta-O semiconductors for driving direct water splitting with visible light.

    Science.gov (United States)

    Wang, Limin; Cao, Bingfei; Kang, Wei; Hybertsen, Mark; Maeda, Kazuhiko; Domen, Kazunari; Khalifah, Peter G

    2013-08-19

    Two new metal oxide semiconductors belonging to the Ag-Bi-M-O (M = Nb, Ta) chemical systems have been synthesized as candidate compounds for driving overall water splitting with visible light on the basis of cosubstitution of Ag and Bi on the A-site position of known Ca2M2O7 pyrochlores. The low-valence band edge energies of typical oxide semiconductors prevents direct water splitting in compounds with band gaps below 3.0 eV, a limitation which these compounds are designed to overcome through the incorporation of low-lying Ag 4d(10) and Bi 6s(2) states into compounds of nominal composition "AgBiM2O7". It was found that the "AgBiTa2O7" pyrochlores are in fact a solid solution with an approximate range of Ag(x)Bi(5/6)Ta2O(6.25+x/2) with 0.5 semiconductors with the onset of strong direct absorption at 2.72 and 2.96 eV, respectively. Electronic structure calculations for an ordered AgBiNb2O7 structure show that the band gap reduction and the elevation of the valence band primarily result from hybridized Ag d(10)-O 2p orbitals that lie at higher energy than the normal O 2p states in typical pyrochlore oxides. While the minimum energy gap is direct in the band structure, the lowest energy dipole allowed optical transitions start about 0.2 eV higher in energy than the minimum energy transition and involve different bands. This suggests that the minimum electronic band gap in these materials is slightly smaller than the onset energy for strong absorption in the optical measurements. The elevated valence band energies of the niobate and tantalate compounds are experimentally confirmed by the ability of these compounds to reduce 2 H(+) to H2 gas when illuminated after functionalization with a Pt cocatalyst.

  2. Electronic Energy Levels and Band Alignment for Aqueous Phenol and Phenolate from First Principles.

    Science.gov (United States)

    Opalka, Daniel; Pham, Tuan Anh; Sprik, Michiel; Galli, Giulia

    2015-07-30

    Electronic energy levels in phenol and phenolate solutions have been computed using density functional theory and many-body perturbation theory. The valence and conduction bands of the solvent and the ionization energies of the solutes have been aligned with respect to the vacuum level based on the concept of a computational standard hydrogen electrode. We have found significant quantitative differences between the generalized-gradient approximation, calculations with the HSE hybrid functional, and many-body perturbation theory in the G0W0 approximation. For phenol, two ionization energies below the photoionization threshold of bulk water have been assigned in the spectrum of Kohn-Sham eigenvalues of the solution. Deprotonation to phenolate was found to lift a third occupied energy level above the valence band maximum of the solvent which is characterized by an electronic lone pair at the hydroxyl group. The second and third ionization energies of phenolate were found to be very similar and explain the intensity pattern observed in recent experiments using liquid-microjet photoemission spectroscopy.

  3. Virtual Distance and Soundstage, and their Impacts on Experienced Emotional Valence

    DEFF Research Database (Denmark)

    Christensen, Justin

    2015-01-01

    stimuli should cause stronger valenced responses in the nearfield than at a distance. Thus, music experienced as being negatively valenced at a distance should be more negatively valenced in nearfield, and music that is experienced as having a positive valence at a distance should be more positively......Research from animal ethology and affective neuroscience suggest that a listener’s perceived distance from a signal source can alter their experienced emotional valence of the music. Furthermore, appraisal theories of emotion suggest that emotionally valenced responses will diverge according...... to the type of emotion presented. For these exploratory investigations, subjects listen to selected musical excerpts on speakers in combination with a tactile transducer attached to their chair. The listening sessions are recorded on EEG supported by subject feedback responses. My hypothesis is that musical...

  4. A High-Speed Power-Line Communication System with Band-Limited OQAM Based Multi-Carrier Transmission

    Science.gov (United States)

    Kawabata, Naohiro; Koga, Hisao; Muta, Osamu; Akaiwa, Yoshihiko

    As a method to realize a high-speed communication in the home network, the power-line communication (PLC) technique is known. A problem of PLC is that leakage radiation interferes with existing systems. When OFDM is used in a PLC system, the leakage radiation is not sufficiently reduced, even if the subcarriers corresponding to the frequency-band of the existing system are never used, because the signal is not strictly band-limited. To solve this problem, each subcarrier must be band-limited. In this paper, we apply the OQAM based multi-carrier transmission (OQAM-MCT) to a high-speed PLC system, where each subcarrier is individually band-limited. We also propose a pilot-symbol sequence suitable for frequency offset estimation, symbol-timing detection and channel estimation in the OQAM-MCT system. In this method, the pilot signal-sequence consists of a repeated series of the same data symbol. With this method, the pilot sequence approximately becomes equivalent to OFDM sequence and therefore existing pilot-assisted methods for OFDM are also applicable to OQAM-MCT system. Computer simulation results show that the OQAM-MCT system achieves both good transmission rate performance and low out-of-band radiation in PLC channels. It is also shown that the proposed pilot-sequence improves frequency offset estimation, symbol-timing detection and channel estimation performance as compared with the case of using pseudo-noise sequence.

  5. Band alignment of InGaZnO4/Si interface by hard x-ray photoelectron spectroscopy

    International Nuclear Information System (INIS)

    Lee, Kyeongmi; Kamiya, Toshio; Nomura, Kenji; Yanagi, Hiroshi; Ikenaga, Eiji; Sugiyama, Takeharu; Kobayashi, Keisuke; Hosono, Hideo

    2012-01-01

    Although amorphous InGaZnO 4 has intensively been studied for a semiconductor channel material of thin-film transistors in next-generation flat-panel displays, its electronic structure parameters have not been reported. In this work, the electron affinities (χ) and the ionization potentials (I p ) of crystalline and amorphous InGaZnO 4 (c-IGZO and a-IGZO) were measured using bulk-sensitive hard x-ray photoelectron spectroscopy. First, the χ and I p values of c-IGZO and a-IGZO thin films were estimated by aligning the Zn 2p 3/2 core level energies to a literature value for ZnO, which provided χ = 3.90 eV and I p = 7.58 eV for c-IGZO and 4.31 eV and 7.41 eV for a-IGZO. It was also confirmed that the escape depth of the photoelectrons excited by the photon energy of 5950.2 eV is 3.3 nm for a-IGZO and large enough for directly measuring the interface electronic structure using a-IGZO/c-Si heterojunctions. It provided the valence band offset of ∼2.3 eV, which agrees well with the above data. The present results substantiate that the a-IGZO/c-Si interface follows well the Schottky-Mott rule.

  6. Intersite interactions and susceptibility in mixed valence systems

    International Nuclear Information System (INIS)

    Xiaoqian Wang; Gao Lin; Bingjian Ni; Fusui Liu.

    1985-10-01

    This paper considers the effect of intersite processes on the susceptibility in mixed valence system. The method of thermodynamical perturbation used in this paper can also be generalized to study other properties of mixed valence system. The general formula of partition function of two-site interactions for the mixed valence system is given. The numerical calculations show that the intersite interaction is large enough to explain the minimum of susceptibility discovered in experiments. The different types of our theoretical curves predict that the susceptibility should exhibit a rich variety of behaviour at low temperature for various materials. (author)

  7. Space-Valence Priming with Subliminal and Supraliminal Words

    Directory of Open Access Journals (Sweden)

    Ulrich eAnsorge

    2013-02-01

    Full Text Available To date it is unclear whether (1 awareness-independent non-evaluative semantic processes influence affective semantics and whether (2 awareness-independent affective semantics influence non-evaluative semantic processing. In the current study, we investigated these questions with the help of subliminal (masked primes and visible targets in a space-valence across-category congruence effect. In line with (1, we found that subliminal space prime words influenced valence classification of supraliminal target words (Experiment 1: Classifications were faster with a congruent prime (e.g., the prime ‘up’ before the target ‘happy’ than with an incongruent prime (e.g., the prime ‘up’ before the target ‘sad’. In contrast to (2, no influence of subliminal valence primes on the classification of supraliminal space targets into up- and down-words was found (Experiment 2. Control conditions showed that standard masked response-priming effects were found with both subliminal prime types, and that an across-category congruence effect was also found with supraliminal valence primes and spatial target words. The final Experiment 3 confirmed that the across-category congruence effect indeed reflected priming of target categorization of a relevant meaning category. Together, the data jointly confirmed prediction (1 that awareness-independent non-evaluative semantic priming influences valence judgments.

  8. Impurity band Mott insulators: a new route to high Tc superconductivity

    Directory of Open Access Journals (Sweden)

    Ganapathy Baskaran

    2008-01-01

    Full Text Available Last century witnessed the birth of semiconductor electronics and nanotechnology. The physics behind these revolutionary developments is certain quantum mechanical behaviour of 'impurity state electrons' in crystalline 'band insulators', such as Si, Ge, GaAs and GaN, arising from intentionally added (doped impurities. The present article proposes that certain collective quantum behaviour of these impurity state electrons, arising from Coulomb repulsions, could lead to superconductivity in a parent band insulator, in a way not suspected before. Impurity band resonating valence bond theory of superconductivity in boron doped diamond, recently proposed by us, suggests possibility of superconductivity emerging from impurity band Mott insulators. We use certain key ideas and insights from the field of high-temperature superconductivity in cuprates and organics. Our suggestion also offers new possibilities in the field of semiconductor electronics and nanotechnology. The current level of sophistication in solid state technology and combinatorial materials science is very well capable of realizing our proposal and discover new superconductors.

  9. Valence, arousal and cognitive control: A voluntary task switching study

    Directory of Open Access Journals (Sweden)

    Jelle eDemanet

    2011-11-01

    Full Text Available The present study focused on the interplay between arousal, valence and cognitive control. To this end, we investigated how arousal and valence associated with affective stimuli influenced cognitive flexibility when switching between tasks voluntarily. Three hypotheses were tested. First, a valence hypothesis that states that the positive valence of affective stimuli will facilitate both global and task-switching performance because of increased cognitive flexibility. Second, an arousal hypothesis that states that arousal, and not valence, will specifically impair task-switching performance by strengthening the previously executed task-set. Third, an attention hypothesis that states that both cognitive and emotional control ask for limited attentional resources, and predicts that arousal will impair both global and task-switching performance. The results showed that arousal affected task-switching but not global performance, possibly by phasic modulations of the noradrenergic system that reinforces the previously executed task. In addition, positive valence only affected global performance but not task-switching performance, possibly by phasic modulations of dopamine that stimulates the general ability to perform in a multitasking environment.

  10. The use of bulk states to accelerate the band edge state calculation of a semiconductor quantum dot

    International Nuclear Information System (INIS)

    Voemel, Christof; Tomov, Stanimire Z.; Wang, Lin-Wang; Marques, Osni A.; Dongarra, Jack J.

    2007-01-01

    We present a new technique to accelerate the convergence of the folded spectrum method in empirical pseudopotential band edge state calculations for colloidal quantum dots. We use bulk band states of the materials constituent of the quantum dot to construct initial vectors and a preconditioner. We apply these to accelerate the convergence of the folded spectrum method for the interior states at the top of the valence and the bottom of the conduction band. For large CdSe quantum dots, the number of iteration steps until convergence decreases by about a factor of 4 compared to previous calculations

  11. Effect of valence on the electromigration in silver

    International Nuclear Information System (INIS)

    Nguyen Van Doan

    1970-01-01

    It is shown that the apparent effective valence Z B ** of a solute deduced from experiments differs from the true effective valence Z B * defined in the atomic models by a corrective term due to the 'vacancy flow effect'. The experimental results suggest that this corrective term is very important and that it is negative for transition elements; this hypothesis is confirmed for the case of iron in a copper matrix. For the elements to the right of silver in the periodic table, where the correction can be neglected, the effective valence of the solute varies linearly with z (z + 1), z being the difference between the valency of the solute and the solvent; in contrast, the further the solute is from the solvent in the periodic table the more nearly the electronic structure of the ion at the saddle point resembles that of the ion at the equilibrium position. (author) [fr

  12. Band alignment of HfO{sub 2}/AlN heterojunction investigated by X-ray photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Ye, Gang [School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Wang, Hong, E-mail: ewanghong@ntu.edu.sg [School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); CNRS-International-NTU-THALES Research Alliances/UMI 3288, 50 Nanyang Drive, Singapore 637553 (Singapore); Ji, Rong [Data Storage Institute, Agency for Science Technology and Research (A-STAR), Singapore 117608 (Singapore)

    2016-04-18

    The band alignment between AlN and Atomic-Layer-Deposited (ALD) HfO{sub 2} was determined by X-ray photoelectron spectroscopy (XPS). The shift of Al 2p core-levels to lower binding energies with the decrease of take-off angles θ indicated upward band bending occurred at the AlN surface. Based on the angle-resolved XPS measurements combined with numerical calculations, valence band discontinuity ΔE{sub V} of 0.4 ± 0.2 eV at HfO{sub 2}/AlN interface was determined by taking AlN surface band bending into account. By taking the band gap of HfO{sub 2} and AlN as 5.8 eV and 6.2 eV, respectively, a type-II band line-up was found between HfO{sub 2} and AlN.

  13. The effect of density-of-state tails on band-to-band tunneling: Theory and application to tunnel field effect transistors

    Science.gov (United States)

    Sant, S.; Schenk, A.

    2017-10-01

    It is demonstrated how band tail states in the semiconductor influence the performance of a Tunnel Field Effect Transistor (TFET). As a consequence of the smoothened density of states (DOS) around the band edges, the energetic overlap of conduction and valence band states occurs gradually at the onset of band-to-band tunneling (BTBT), thus degrading the sub-threshold swing (SS) of the TFET. The effect of the band tail states on the current-voltage characteristics is modelled quantum-mechanically based on the idea of zero-phonon trap-assisted tunneling between band and tail states. The latter are assumed to arise from a 3-dimensional pseudo-delta potential proposed by Vinogradov [1]. This model potential allows the derivation of analytical expressions for the generation rate covering the whole range from very strong to very weak localization of the tail states. Comparison with direct BTBT in the one-band effective mass approximation reveals the essential features of tail-to-band tunneling. Furthermore, an analytical solution for the problem of tunneling from continuum states of the disturbed DOS to states in the opposite band is found, and the differences to direct BTBT are worked out. Based on the analytical expressions, a semi-classical model is implemented in a commercial device simulator which involves numerical integration along the tunnel paths. The impact of the tail states on the device performance is analyzed for a nanowire Gate-All-Around TFET. The simulations show that tail states notably impact the transfer characteristics of a TFET. It is found that exponentially decaying band tails result in a stronger degradation of the SS than tail states with a Gaussian decay of their density. The developed model allows more realistic simulations of TFETs including their non-idealities.

  14. The acoustic correlates of valence depend on emotion family.

    Science.gov (United States)

    Belyk, Michel; Brown, Steven

    2014-07-01

    The voice expresses a wide range of emotions through modulations of acoustic parameters such as frequency and amplitude. Although the acoustics of individual emotions are well understood, attempts to describe the acoustic correlates of broad emotional categories such as valence have yielded mixed results. In the present study, we analyzed the acoustics of emotional valence for different families of emotion. We divided emotional vocalizations into "motivational," "moral," and "aesthetic" families as defined by the OCC (Ortony, Clore, and Collins) model of emotion. Subjects viewed emotional scenarios and were cued to vocalize congruent exclamations in response to them, for example, "Yay!" and "Damn!". Positive valence was weakly associated with high-pitched and loud vocalizations. However, valence interacted with emotion family for both pitch and amplitude. A general acoustic code for valence does not hold across families of emotion, whereas family-specific codes provide a more accurate description of vocal emotions. These findings are consolidated into a set of "rules of expression" relating vocal dimensions to emotion dimensions. Copyright © 2014 The Voice Foundation. Published by Mosby, Inc. All rights reserved.

  15. Emissions trading with offset markets and free quota allocations

    Energy Technology Data Exchange (ETDEWEB)

    Rosendahl, Knut Einar; Strand, Jon

    2012-07-01

    We study interactions between a 'policy bloc's' emissions quota market and an offset market where emissions offsets can be purchased from a non-policy 'fringe' of countries (such as for the CDM under the Kyoto Protocol). Policy-bloc firms are assumed to benefit from free quota allocations that are updated according to either past emissions or past outputs. We show that both overall abatement, and the allocation of given abatement between the policy bloc and the fringe, tend to be inefficient. When the policy-bloc quota market and offset markets are fully integrated (and firms buy offsets directly from the fringe), and all quotas and offsets must be traded at a single price, it is optimal for the policy bloc to either not constrain the offset market whatsoever, or to ban offsets completely. The former (latter) case occurs when free allocation of quotas is not too generous (very generous), and the offset market can profitably deliver large (only a small) quota amounts. Governments of policy countries would however instead prefer to buy offsets directly from the fringe at a price below the policy-bloc quota price. The offset price will then be below the marginal damage cost of emissions, and the quota price in the policy bloc above marginal damage cost. This solution is also inefficient as the policy bloc (acting as a monopsonist) purchases too few offsets from the fringe.(Author)

  16. Dimensionality and its effects upon the valence electronic structure of ordered metallic systems

    International Nuclear Information System (INIS)

    Tobin, J.G.

    1983-07-01

    The system c(10x2)Ag/Cu(001) was investigated with Angle-Resolved Photoemission (ARP), Low Energy Electron Diffraction (LEED) and Auger Electron Spectroscopy (AES). LEED and AES provided the calibration of a quartz microbalance used to measure the amount of silver evaporated onto the copper single crystal and also established the monolayer geometrical structure at one monolayer exposure. An off-normal ARP bandmapping study performed with polarized HeI and NeI radiation demonstrated the electronically two-dimensional nature of the silver d-bands at coverages of near one monolayer. The states at the surface Brillouin Zone center were assigned upon the basis of their polarization dependences and a structural model of hexagonal symmetry. A normal emission ARP experiment was performed at the Stanford Synchrotron Radiation Laboratory (SSRL) over the photon energy range of 6 to 32 eV. Data from it documented the evolution of the valence electronic structure of the silver overlayer from a two-dimensional hexagonal valence to a three-dimensional behavior converging towards that of bulk Ag(111). A structural study was attempted using the ARP technique of Normal Emission Photoelectron Diffraction over the photon energy range of 3.4 to 3.7 keV at SSRL, the results of which are inconclusive

  17. Interfacial chemistry and energy band alignment of TiAlO on 4H-SiC determined by X-ray photoelectron spectroscopy

    International Nuclear Information System (INIS)

    Wang, Qian; Cheng, Xinhong; Zheng, Li; Ye, Peiyi; Li, Menglu; Shen, Lingyan; Li, Jingjie; Zhang, Dongliang; Gu, Ziyue; Yu, Yuehui

    2017-01-01

    Highlights: • Composite TiAlO rather than TiO_2-Al_2O_3 laminations is deposited on 4H-SiC by PEALD. • An interfacial layer composed of Ti, Si, O and C forms between TiAlO and 4H-SiC. • TiAlO offers competitive barrier heights (>1 eV) for both electrons and holes. - Abstract: Intermixing of TiO_2 with Al_2O_3 to form TiAlO films on 4H-SiC is expected to simultaneously boost the dielectric constant and achieve sufficient conduction/valence band offsets (CBO/VBO) between dielectrics and 4H-SiC. In this work, a composite TiAlO film rather than TiO_2-Al_2O_3 laminations is deposited on 4H-SiC by plasma enhanced atomic layer deposition (PEALD). X-ray photoelectron spectroscopy (XPS) is performed to systematically analyze the interfacial chemistry and energy band alignment between TiAlO and 4H-SiC. An interfacial layer composed of Ti, Si, O and C forms between TiAlO and 4H-SiC during PEALD process. The VBO and CBO between TiAlO and 4H-SiC are determined to be 1.45 eV and 1.10 eV, respectively, which offer competitive barrier heights (>1 eV) for both electrons and holes and make it suitable for the fabrication of 4H-SiC metal-oxide-semiconductor field effect transistors (MOSFETs).

  18. Interfacial chemistry and energy band alignment of TiAlO on 4H-SiC determined by X-ray photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Qian [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-System & Information Technology, Chinese Academy of Sciences, Changning Road 865, Shanghai 200050 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Cheng, Xinhong, E-mail: xh_cheng@mail.sim.ac.cn [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-System & Information Technology, Chinese Academy of Sciences, Changning Road 865, Shanghai 200050 (China); Zheng, Li, E-mail: zhengli@mail.sim.ac.cn [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-System & Information Technology, Chinese Academy of Sciences, Changning Road 865, Shanghai 200050 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Ye, Peiyi; Li, Menglu [Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095 (United States); Shen, Lingyan; Li, Jingjie; Zhang, Dongliang; Gu, Ziyue [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-System & Information Technology, Chinese Academy of Sciences, Changning Road 865, Shanghai 200050 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Yu, Yuehui [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-System & Information Technology, Chinese Academy of Sciences, Changning Road 865, Shanghai 200050 (China)

    2017-07-01

    Highlights: • Composite TiAlO rather than TiO{sub 2}-Al{sub 2}O{sub 3} laminations is deposited on 4H-SiC by PEALD. • An interfacial layer composed of Ti, Si, O and C forms between TiAlO and 4H-SiC. • TiAlO offers competitive barrier heights (>1 eV) for both electrons and holes. - Abstract: Intermixing of TiO{sub 2} with Al{sub 2}O{sub 3} to form TiAlO films on 4H-SiC is expected to simultaneously boost the dielectric constant and achieve sufficient conduction/valence band offsets (CBO/VBO) between dielectrics and 4H-SiC. In this work, a composite TiAlO film rather than TiO{sub 2}-Al{sub 2}O{sub 3} laminations is deposited on 4H-SiC by plasma enhanced atomic layer deposition (PEALD). X-ray photoelectron spectroscopy (XPS) is performed to systematically analyze the interfacial chemistry and energy band alignment between TiAlO and 4H-SiC. An interfacial layer composed of Ti, Si, O and C forms between TiAlO and 4H-SiC during PEALD process. The VBO and CBO between TiAlO and 4H-SiC are determined to be 1.45 eV and 1.10 eV, respectively, which offer competitive barrier heights (>1 eV) for both electrons and holes and make it suitable for the fabrication of 4H-SiC metal-oxide-semiconductor field effect transistors (MOSFETs).

  19. Prediction of valence and arousal from music features

    NARCIS (Netherlands)

    Den Brinker, A.C.; Van Dinther, C.H.B.A.; Skowronek, J.

    2011-01-01

    Mood is an important attribute of music and knowledge on mood can beused as a basic ingredient in music recommender and retrieval systems. Moods are assumed to be dominantly determined by two dimensions:valence and arousal. An experiment was conducted to attain data forsong-based ratings of valence

  20. Terahertz optical-Hall effect for multiple valley band materials: n-type silicon

    International Nuclear Information System (INIS)

    Kuehne, P.; Hofmann, T.; Herzinger, C.M.; Schubert, M.

    2011-01-01

    The optical-Hall effect comprises generalized ellipsometry at long wavelengths on samples with free-charge carriers placed within external magnetic fields. Measurement of the anisotropic magneto-optic response allows for the determination of the free-charge carrier properties including spatial anisotropy. In this work we employ the optical-Hall effect at terahertz frequencies for analysis of free-charge carrier properties in multiple valley band materials, for which the optical free-charge carrier contributions originate from multiple Brillouin-zone conduction or valence band minima or maxima, respectively. We investigate exemplarily the room temperature optical-Hall effect in low phosphorous-doped n-type silicon where free electrons are located in six equivalent conduction-band minima near the X-point. We simultaneously determine their free-charge carrier concentration, mobility, and longitudinal and transverse effective mass parameters.

  1. Ab-initio valence band spectra of Al, In doped ZnO

    International Nuclear Information System (INIS)

    Palacios, P.; Sanchez, K.; Wahnon, P.

    2009-01-01

    We present the structural and electronic characterization of n-doped (Aluminium or Indium) ZnO and the effect of the doping on the calculated photoelectron spectroscopy (PES) spectra. The fully-relaxed calculations have been made using the density functional theory, including a Hubbard correlation term that increases the Zn-3d states binding energy, and which matches the experimental values. The effect of Oxygen vacancies is also included in our study. Our results show that the new Al or In-donor levels appearing in the conduction band hybridize with the Oxygen-2p states and help decrease the resistivity of these doped systems as was found experimentally. The calculated PES spectra show a small enhancement in the intensity close to the chemical potential as a result of these new Al or In levels

  2. Valence photoelectron spectrum of KBr: Effects of electron correlation

    International Nuclear Information System (INIS)

    Calo, A.; Huttula, M.; Patanen, M.; Aksela, H.; Aksela, S.

    2008-01-01

    The valence photoelectron spectrum has been measured for molecular KBr. Experimental energies of the main and satellite structures have been compared with the results of ab initio calculations based on molecular orbital theory including configuration and multiconfiguration interaction approaches. Comparison between the experimental KBr spectrum and previously reported Kr valence photoelectron spectrum has also been performed in order to find out if electron correlation is of the same importance in the valence ionized state of KBr as in the corresponding state of Kr

  3. Valence QCD: Connecting QCD to the quark model

    International Nuclear Information System (INIS)

    Liu, K.F.; Dong, S.J.; Draper, T.; Sloan, J.; Leinweber, D.; Woloshyn, R.M.

    1999-01-01

    A valence QCD theory is developed to study the valence quark properties of hadrons. To keep only the valence degrees of freedom, the pair creation through the Z graphs is deleted in the connected insertions, whereas the sea quarks are eliminated in the disconnected insertions. This is achieved with a new 'valence QCD' Lagrangian where the action in the time direction is modified so that the particle and antiparticle decouple. It is shown in this valence version of QCD that the ratios of isovector to isoscalar matrix elements (e.g., F A /D A and F S /D S ratios) in the nucleon reproduce the SU(6) quark model predictions in a lattice QCD calculation. We also consider how the hadron masses are affected on the lattice and discover new insights into the origin of dynamical mass generation. It is found that, within statistical errors, the nucleon and the Δ become degenerate for the quark masses we have studied (ranging from 1 to 4 times the strange mass). The π and ρ become nearly degenerate in this range. It is shown that valence QCD has the C, P, T symmetries. The lattice version is reflection positive. It also has the vector and axial symmetries. The latter leads to a modified partially conserved axial Ward identity. As a result, the theory has a U(2N F ) symmetry in the particle-antiparticle space. Through lattice simulation, it appears that this is dynamically broken down to U q (N F )xU bar q (N F ). Furthermore, the lattice simulation reveals spin degeneracy in the hadron masses and various matrix elements. This leads to an approximate U q (2N F )xU bar q (2N F ) symmetry which is the basis for the valence quark model. In addition, we find that the masses of N, Δ,ρ,π,a 1 , and a 0 all drop precipitously compared to their counterparts in the quenched QCD calculation. This is interpreted as due to the disappearance of the 'constituent' quark mass which is dynamically generated through tadpole diagrams. The origin of the hyperfine splitting in the baryon is

  4. Processing negative valence of word pairs that include a positive word.

    Science.gov (United States)

    Itkes, Oksana; Mashal, Nira

    2016-09-01

    Previous research has suggested that cognitive performance is interrupted by negative relative to neutral or positive stimuli. We examined whether negative valence affects performance at the word or phrase level. Participants performed a semantic decision task on word pairs that included either a negative or a positive target word. In Experiment 1, the valence of the target word was congruent with the overall valence conveyed by the word pair (e.g., fat kid). As expected, response times were slower in the negative condition relative to the positive condition. Experiment 2 included target words that were incongruent with the overall valence of the word pair (e.g., fat salary). Response times were longer for word pairs whose overall valence was negative relative to positive, even though these word pairs included a positive word. Our findings support the Cognitive Primacy Hypothesis, according to which emotional valence is extracted after conceptual processing is complete.

  5. Fluorescence properties of valence-controlled Eu{sup 2+} and Mn{sup 2+} ions in aluminosilicate glasses

    Energy Technology Data Exchange (ETDEWEB)

    Van Tuyen, Ho [Duy Tan University, 3 Quang Trung, Hai Chau, Da Nang (Viet Nam); Nonaka, Takamasa; Yamanaka, Ken-ichi [Toyota Central R& D Labs., Inc., Nagakute, Aichi (Japan); Chau, Pham Minh; Quy Hai, Nguyen Thi; Quang, Vu Xuan [Duy Tan University, 3 Quang Trung, Hai Chau, Da Nang (Viet Nam); Nogami, Masayuki, E-mail: mnogami@mtj.biglobe.ne.jp [Toyota Physical and Chemical Research Institute, Nagakute, Aichi (Japan); Ton Duc Thang University, Ho Chi Minh City (Viet Nam); Duy Tan University, 3 Quang Trung, Hai Chau, Da Nang (Viet Nam)

    2017-04-15

    Controlling of valence states of metal ions doped in glasses has attracted considerable interest due to the possibility of looking toward optical applications. In this study, new Na{sub 2}O-Al{sub 2}O{sub 3}-SiO{sub 2} glasses were developed to dope Eu{sup 2+} and Mn{sup 2+} with well controlled valence states by heating in H{sub 2} gas atmosphere, and the changes in the valence state of doped-ions and their fluorescence properties were investigated using visible and infrared optical absorption spectroscopies, X-ray absorption fine structure spectroscopy, and fluorescence spectroscopy. Among Eu{sup 3+}, Mn{sup 3+} and Mn{sup 2+} ions incorporated in the as-prepared glasses, the Eu{sup 3+} and Mn{sup 3+} ions were reduced to Eu{sup 2+} and Mn{sup 2+} ions, respectively, by heating in H{sub 2} gas and OH bonds were concurrently formed. The fluorescence spectra of glasses heated in H{sub 2} exhibited broad emission bands at 450 and 630 nm wavelength, assigned to the Eu{sup 2+} and Mn{sup 2+}, respectively, ions, in which the fluorescence intensity at 450 nm was observed to decrease with increasing Mn{sup 2+} ion content. The increased fluorescence intensities were analyzed as the energy transfer from Eu{sup 2+} to Mn{sup 2+} ions and the energy transfer efficiency was estimated with a concentration of Eu{sup 2+}and Mn{sup 2+} ions.

  6. 22 CFR 1007.8 - Procedures for salary offset.

    Science.gov (United States)

    2010-04-01

    ... 22 Foreign Relations 2 2010-04-01 2010-04-01 true Procedures for salary offset. 1007.8 Section 1007.8 Foreign Relations INTER-AMERICAN FOUNDATION SALARY OFFSET § 1007.8 Procedures for salary offset... final salary or leave payments in accordance with 31 U.S.C. 3716. ...

  7. Reducing the negative valence of stressful memories through emotionally valenced, modality-specific tasks

    NARCIS (Netherlands)

    Tadmor, Avia; McNally, Richard J; Engelhard, Iris M

    2016-01-01

    BACKGROUND AND OBJECTIVES: People who perform a cognitively demanding secondary task while recalling a distressing memory often experience the memory as less emotional, vivid, or accurate during subsequent recollections. In this experiment, we tested whether the emotional valence (positive versus

  8. 17 CFR 141.8 - Procedures for salary offset.

    Science.gov (United States)

    2010-04-01

    ... 17 Commodity and Securities Exchanges 1 2010-04-01 2010-04-01 false Procedures for salary offset. 141.8 Section 141.8 Commodity and Securities Exchanges COMMODITY FUTURES TRADING COMMISSION SALARY OFFSET § 141.8 Procedures for salary offset. (a) Deductions to liquidate an employee's debt will be by...

  9. 38 CFR 1.992 - Procedures for salary offset.

    Science.gov (United States)

    2010-07-01

    ... 38 Pensions, Bonuses, and Veterans' Relief 1 2010-07-01 2010-07-01 false Procedures for salary offset. 1.992 Section 1.992 Pensions, Bonuses, and Veterans' Relief DEPARTMENT OF VETERANS AFFAIRS GENERAL PROVISIONS Salary Offset Provisions § 1.992 Procedures for salary offset. (a) Types of collection...

  10. 22 CFR 34.16 - Procedures for salary offset.

    Science.gov (United States)

    2010-04-01

    ... 22 Foreign Relations 1 2010-04-01 2010-04-01 false Procedures for salary offset. 34.16 Section 34.16 Foreign Relations DEPARTMENT OF STATE CLAIMS AND STOLEN PROPERTY DEBT COLLECTION Salary Offset § 34.16 Procedures for salary offset. Unless otherwise provided by statute or contract, the following...

  11. Synchrotron-radiation photoemission study of CdS/CuInSe2 heterojunction formation

    International Nuclear Information System (INIS)

    Nelson, A.J.; Gebhard, S.; Rockett, A.; Colavita, E.; Engelhardt, M.; Hoechst, H.

    1990-01-01

    Synchrotron-radiation soft-x-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS/CuInSe 2 heterojunction interface. CdS overlayers were deposited in steps on single-crystal p- and n-type CuInSe 2 at 250 degree C. Results indicate that the CdS grows in registry with the substrate, initially in a two-dimensional growth mode followed by three-dimensional island growth as is corroborated by reflection high-energy electron-diffraction analysis. Photoemission measurements were acquired after each growth in order to observe changes in the valence-band electronic structure as well as changes in the In 4d, Se 3d, Cd 4d, and S 2p core lines. The results were used to correlate the interface chemistry with the electronic structure at these interfaces and to directly determine the CdS/CuInSe 2 heterojunction valence-band discontinuity and the consequent heterojunction band diagram. These results show that the Katnani-Margaritondo method is unreliable in determining offsets for heterojunctions where significant Fermi-level pinning may occur and where the local structure and chemistry of the interface depends strongly on the specific heterojunction

  12. Valence, magnetism and conduction in the intermediate valence compounds: the case SmB6

    International Nuclear Information System (INIS)

    Derr, J.

    2006-09-01

    In some rare earth based compounds, the 4f level is situated so close to the Fermi level that the valence of the compound can become intermediate between two integer values. The so called 'intermediate valence' compound of Samarium hexaboride (SmB 6 ) is one typical example of the exciting physics which can result from this quantum equilibrium between two valence configurations. The first configuration (Sm 2+ ) corresponds to an insulating and non magnetic state whereas the second one (Sm 3+ ) would theoretically give a magnetic and metallic ground state. This dissertation deals with the influence of pressure on this equilibrium. Specific heat measurements under pressure evidenced a new long range magnetic ordering for pressures higher than p c ∼ 10 GPa. On another hand, transport measurements measured for the first time in good conditions of hydrostatics found a reliable and reproducible critical pressure for the insulator to metal transition equal to p c . The phase diagram of SmB 6 is now well known and the observation for the first time of a magnetic anomaly in the high pressure resistivity curves certifies that the onset of the magnetic phase really coincide with the closure of the gap. This change at the critical pressure p c is discussed in a general frame taking into account the Kondo lattice temperature as a key parameter for the renormalization of the wavefunction from one integer configuration to the other whereas the valence itself is still intermediate. This general idea seems to be valid also for other systems studied in this dissertation like SmS or TmSe and could even be valid for more general cases (Ytterbium, Cerium). In the same time, resistivity measurements under uniaxial stress were undertaken. The result is a strong anisotropy effect observed on the pressure dependence of the residual resistivity in the compound SmB 6 . The comparison with the transport under hydrostatic conditions enables us to consider a new idea for the nature of the gap

  13. Explaining the effect of event valence on unrealistic optimism.

    Science.gov (United States)

    Gold, Ron S; Brown, Mark G

    2009-05-01

    People typically exhibit 'unrealistic optimism' (UO): they believe they have a lower chance of experiencing negative events and a higher chance of experiencing positive events than does the average person. UO has been found to be greater for negative than positive events. This 'valence effect' has been explained in terms of motivational processes. An alternative explanation is provided by the 'numerosity model', which views the valence effect simply as a by-product of a tendency for likelihood estimates pertaining to the average member of a group to increase with the size of the group. Predictions made by the numerosity model were tested in two studies. In each, UO for a single event was assessed. In Study 1 (n = 115 students), valence was manipulated by framing the event either negatively or positively, and participants estimated their own likelihood and that of the average student at their university. In Study 2 (n = 139 students), valence was again manipulated and participants again estimated their own likelihood; additionally, group size was manipulated by having participants estimate the likelihood of the average student in a small, medium-sized, or large group. In each study, the valence effect was found, but was due to an effect on estimates of own likelihood, not the average person's likelihood. In Study 2, valence did not interact with group size. The findings contradict the numerosity model, but are in accord with the motivational explanation. Implications for health education are discussed.

  14. Band-to-band tunneling in Γ valley for Ge source lateral tunnel field effect transistor: Thickness scaling

    Science.gov (United States)

    Jain, Prateek; Rastogi, Priyank; Yadav, Chandan; Agarwal, Amit; Chauhan, Yogesh Singh

    2017-07-01

    The direct and indirect valleys in Germanium (Ge) are separated by a very small offset, which opens up the prospect of direct tunneling in the Γ valley of an extended Ge source tunnel field effect transistor (TFET). We explore the impact of thickness scaling of extended Ge source lateral TFET on the band to band tunneling (BTBT) current. The Ge source is extended inside the gate by 2 nm to confine the tunneling in Ge only. We observe that as the thickness is scaled, the band alignment at the Si/Ge heterojunction changes significantly, which results in an increase in Ge to Si BTBT current. Based on density functional calculations, we first obtain the band structure parameters (bandgap, effective masses, etc.) for the Ge and Si slabs of varying thickness, and these are then used to obtain the thickness dependent Kane's BTBT tunneling parameters. We find that electrostatics improves as the thickness is reduced in the ultra-thin Ge film ( ≤ 10 nm). The ON current degrades as we scale down in thickness; however, the subthreshold slope ( S S AVG ) improves remarkably with thickness scaling due to subsurface BTBT. We predict that 8 nm thin devices offer the best option for optimized ON current and S S AVG .

  15. 16 CFR 1027.8 - Procedures for salary offset.

    Science.gov (United States)

    2010-01-01

    ... 16 Commercial Practices 2 2010-01-01 2010-01-01 false Procedures for salary offset. 1027.8 Section 1027.8 Commercial Practices CONSUMER PRODUCT SAFETY COMMISSION GENERAL SALARY OFFSET § 1027.8 Procedures for salary offset. (a) Deductions to liquidate an employee's debt will be by the method and in the...

  16. 5 CFR 1215.8 - Procedures for salary offset.

    Science.gov (United States)

    2010-01-01

    ... 5 Administrative Personnel 3 2010-01-01 2010-01-01 false Procedures for salary offset. 1215.8... MANAGEMENT Salary Offset § 1215.8 Procedures for salary offset. (a) Deductions to liquidate an employee's... payment due to a separated employee including but not limited to final salary payment or leave in...

  17. 45 CFR 607.8 - Procedures for salary offset.

    Science.gov (United States)

    2010-10-01

    ... 45 Public Welfare 3 2010-10-01 2010-10-01 false Procedures for salary offset. 607.8 Section 607.8 Public Welfare Regulations Relating to Public Welfare (Continued) NATIONAL SCIENCE FOUNDATION SALARY OFFSET § 607.8 Procedures for salary offset. (a) Deductions to liquidate an employee's debt will be by...

  18. 32 CFR 1697.8 - Procedures for salary offset.

    Science.gov (United States)

    2010-07-01

    ... 32 National Defense 6 2010-07-01 2010-07-01 false Procedures for salary offset. 1697.8 Section 1697.8 National Defense Other Regulations Relating to National Defense SELECTIVE SERVICE SYSTEM SALARY OFFSET § 1697.8 Procedures for salary offset. (a) Deductions to liquidate an employee's debt will be by...

  19. 14 CFR 1261.603 - Procedures for salary offset.

    Science.gov (United States)

    2010-01-01

    ... 14 Aeronautics and Space 5 2010-01-01 2010-01-01 false Procedures for salary offset. 1261.603... salary offset. If NASA is both the paying and creditor agency, the following requirements must be met... of the debt through salary offset by deductions from the employee's current disposable pay, stating...

  20. 5 CFR 179.212 - Procedures for salary offset.

    Science.gov (United States)

    2010-01-01

    ... 5 Administrative Personnel 1 2010-01-01 2010-01-01 false Procedures for salary offset. 179.212... COLLECTION STANDARDS Salary Offset § 179.212 Procedures for salary offset. (a) The Director or his or her designee shall coordinate salary deductions under this subpart. (b) OPM payroll office shall determine the...

  1. 47 CFR 1.1951 - Offset against tax refunds.

    Science.gov (United States)

    2010-10-01

    ... 47 Telecommunication 1 2010-10-01 2010-10-01 false Offset against tax refunds. 1.1951 Section 1... Claims Owed the United States Cooperation with the Internal Revenue Service § 1.1951 Offset against tax refunds. The Commission will take action to effect administrative offset against tax refunds due to...

  2. Governing the carbon offset market

    OpenAIRE

    Lovell, Heather C.

    2010-01-01

    Carbon offsets are produced and sold under the international climate change regime (the United Nations Kyoto Protocol) and also within an expanding voluntary offset market in which companies and individuals can voluntarily opt to compensate for their greenhouse gas emissions. The volume of carbon produced and consumed within compliance and voluntary markets has grown dramatically in the last 5 years, raising a number of governance challenges. This Focus Article gives an overview of the govern...

  3. What is the band alignment of Cu2ZnSn(S,Se)4 solar cells?

    DEFF Research Database (Denmark)

    Crovetto, Andrea; Hansen, Ole

    2017-01-01

    The band alignment at the Cu2ZnSn(S,Se)4/CdS solar cell heterojunction is a controversial issue, as different measurements and calculations point to substantially different conduction band offsets (CBO). As the actual value of the CBO has profound implications on solar cell performance, the aim...... of this work is to separate genuine process-dependent variations in the CBO from errors in its experimental determination. We argue that the two most likely mechanisms responsible for real CBO variations are Fermi level pinning (which tends to decrease the CBO) and chemical interdiffusion (which tends...... measurement approaches. Interestingly, a rough correlation can be established between the CBO measured at the Cu2ZnSnS4/CdS interface by different groups and their corresponding solar cell efficiency: lower-efficiency cells often have a large "cliff-like" offset, whereas most high-efficiency cells have...

  4. Valence bond model potential energy surface for H4

    International Nuclear Information System (INIS)

    Silver, D.M.; Brown, N.J.

    1980-01-01

    Potential energy surfaces for the H 4 system are derived using the valence bond procedure. An ab initio evaluation of the valence bond energy expression is described and some of its numerical properties are given. Next, four semiempirical evaluations of the valence bond energy are defined and parametrized to yield reasonable agreement with various ab initio calculations of H 4 energies. Characteristics of these four H 4 surfaces are described by means of tabulated energy minima and equipotential contour maps for selected geometrical arrangements of the four nuclei

  5. Effect of the valence electron concentration on the bulk modulus and chemical bonding in Ta2AC and Zr2AC (A=Al, Si, and P)

    International Nuclear Information System (INIS)

    Schneider, Jochen M.; Music, Denis; Sun Zhimei

    2005-01-01

    We have studied the effect of the valence electron concentration, on the bulk modulus and the chemical bonding in Ta 2 AC and Zr 2 AC (A=Al, Si, and P) by means of ab initio calculations. Our equilibrium volume and the hexagonal ratio (c/a) agree well (within 2.7% and 1.2%, respectively) with previously published experimental data for Ta 2 AlC. The bulk moduli of both Ta 2 AC and Zr 2 AC increase as Al is substituted with Si and P by 13.1% and 20.1%, respectively. This can be understood since the substitution is associated with an increased valence electron concentration, resulting in band filling and an extensive increase in cohesion

  6. 8-band and 14-band kp modeling of electronic band structure and material gain in Ga(In)AsBi quantum wells grown on GaAs and InP substrates

    Energy Technology Data Exchange (ETDEWEB)

    Gladysiewicz, M.; Wartak, M. S. [Faculty of Fundamental Problems of Technology, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland); Department of Physics and Computer Science, Wilfrid Laurier University, Waterloo, Ontario N2L 3C5 (Canada); Kudrawiec, R. [Faculty of Fundamental Problems of Technology, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland)

    2015-08-07

    The electronic band structure and material gain have been calculated for GaAsBi/GaAs quantum wells (QWs) with various bismuth concentrations (Bi ≤ 15%) within the 8-band and 14-band kp models. The 14-band kp model was obtained by extending the standard 8-band kp Hamiltonian by the valence band anticrossing (VBAC) Hamiltonian, which is widely used to describe Bi-related changes in the electronic band structure of dilute bismides. It has been shown that in the range of low carrier concentrations n < 5 × 10{sup 18 }cm{sup −3}, material gain spectra calculated within 8- and 14-band kp Hamiltonians are similar. It means that the 8-band kp model can be used to calculate material gain in dilute bismides QWs. Therefore, it can be applied to analyze QWs containing new dilute bismides for which the VBAC parameters are unknown. Thus, the energy gap and electron effective mass for Bi-containing materials are used instead of VBAC parameters. The electronic band structure and material gain have been calculated for 8 nm wide GaInAsBi QWs on GaAs and InP substrates with various compositions. In these QWs, Bi concentration was varied from 0% to 5% and indium concentration was tuned in order to keep the same compressive strain (ε = 2%) in QW region. For GaInAsBi/GaAs QW with 5% Bi, gain peak was determined to be at about 1.5 μm. It means that it can be possible to achieve emission at telecommunication windows (i.e., 1.3 μm and 1.55 μm) for GaAs-based lasers containing GaInAsBi/GaAs QWs. For GaInAsBi/Ga{sub 0.47}In{sub 0.53}As/InP QWs with 5% Bi, gain peak is predicted to be at about 4.0 μm, i.e., at the wavelengths that are not available in current InP-based lasers.

  7. Band gap of corundumlike α -Ga2O3 determined by absorption and ellipsometry

    Science.gov (United States)

    Segura, A.; Artús, L.; Cuscó, R.; Goldhahn, R.; Feneberg, M.

    2017-07-01

    The electronic structure near the band gap of the corundumlike α phase of Ga2O3 has been investigated by means of optical absorption and spectroscopic ellipsometry measurements in the ultraviolet (UV) range (400-190 nm). The absorption coefficient in the UV region and the imaginary part of the dielectric function exhibit two prominent absorption thresholds with wide but well-defined structures at 5.6 and 6.3 eV which have been ascribed to allowed direct transitions from crystal-field split valence bands to the conduction band. Excitonic effects with large Gaussian broadening are taken into account through the Elliott-Toyozawa model, which yields an exciton binding energy of 110 meV and direct band gaps of 5.61 and 6.44 eV. The large broadening of the absorption onset is related to the slightly indirect character of the material.

  8. Correlation between electronic structure and energy band in Eu-doped CuInTe2 semiconductor compound with chalcopyrite structure

    Institute of Scientific and Technical Information of China (English)

    Tai Wang; Yong-Quan Guo; Shuai Li

    2017-01-01

    The Eu-doped Cu(In,Eu)Te2 semiconductors with chalcopyrite structures are promising materials for their applications in the absorption layer for thin-film solar cells due to their wider band-gaps and better optical properties than those of CulnTe2.In this paper,the Eu-doped CulnTe2 (Culn1-xEuxTe2,x =0,0.1,0.2,0.3) are studied systemically based on the empirical electron theory (EET).The studies cover crystal structures,bonding regularities,cohesive energies,energy levels,and valence electron structures.The theoretical values fit the experimental results very well.The physical mechanism of a broadened band-gap induced by Eu doping into CuInTe2 is the transitions between different hybridization energy levels induced by electron hopping between s and d orbitals and the transformations from the lattice electrons to valence electrons for Cu and In ions.The research results reveal that the photovoltaic effect induces the increase of lattice electrons of In and causes the electric resistivity to decrease.The Eu doping into CuInTe2 mainly influences the transition between different hybridization energy levels for Cu atoms,which shows that the 3d electron numbers of Cu atoms change before and after Eu doping.In single phase CuIn1-xEuxTe2,the number of valence electrons changes regularly with increasing Eu content,and the calculated band gap Eg also increases,which implies that the optical properties of Eu-doped CuIn1-xEuxTe2 are improved.

  9. 29 CFR 1650.110 - Implementation of salary offset.

    Science.gov (United States)

    2010-07-01

    ... 29 Labor 4 2010-07-01 2010-07-01 false Implementation of salary offset. 1650.110 Section 1650.110... Procedures for the Collection of Debts by Salary Offset § 1650.110 Implementation of salary offset. (a... proposed voluntary repayment agreement, deductions will begin in the next bi-weekly salary payment after a...

  10. 45 CFR 33.10 - Procedures for salary offset.

    Science.gov (United States)

    2010-10-01

    ... 45 Public Welfare 1 2010-10-01 2010-10-01 false Procedures for salary offset. 33.10 Section 33.10 Public Welfare DEPARTMENT OF HEALTH AND HUMAN SERVICES GENERAL ADMINISTRATION SALARY OFFSET § 33.10 Procedures for salary offset. (a) Method and source of deductions. Unless the employee and the Secretary have...

  11. In-medium pion valence distributions in a light-front model

    Energy Technology Data Exchange (ETDEWEB)

    Melo, J.P.B.C. de, E-mail: joao.mello@cruzeirodosul.edu.br [Laboratório de Física Teórica e Computacional – LFTC, Universidade Cruzeiro do Sul, 01506-000 São Paulo (Brazil); Tsushima, K. [Laboratório de Física Teórica e Computacional – LFTC, Universidade Cruzeiro do Sul, 01506-000 São Paulo (Brazil); Ahmed, I. [Laboratório de Física Teórica e Computacional – LFTC, Universidade Cruzeiro do Sul, 01506-000 São Paulo (Brazil); National Center for Physics, Quaidi-i-Azam University Campus, Islamabad 45320 (Pakistan)

    2017-03-10

    Pion valence distributions in nuclear medium and vacuum are studied in a light-front constituent quark model. The in-medium input for studying the pion properties is calculated by the quark-meson coupling model. We find that the in-medium pion valence distribution, as well as the in-medium pion valence wave function, are substantially modified at normal nuclear matter density, due to the reduction in the pion decay constant.

  12. Multilayer graphene growth on polar dielectric substrates using chemical vapour deposition

    Science.gov (United States)

    Karamat, S.; Çelik, K.; Shah Zaman, S.; Oral, A.

    2018-06-01

    High quality of graphene is necessary for its applications at industrial scale production. The most convenient way is its direct growth on dielectrics which avoid the transfer route of graphene from metal to dielectric substrate usually followed by graphene community. The choice of a suitable dielectric for the gate material which can replace silicon dioxide (SiO2) is in high demand. Various properties like permittivity, thermodynamic stability, film morphology, interface quality, bandgap and band alignment of other dielectrics with graphene needs more exploration. A potential dielectric material is required which could be used to grow graphene with all these qualities. Direct growth of graphene on magnesium oxide (MgO) substrates is an interesting idea and will be a new addition in the library of 2D materials. The present work is about the direct growth of graphene on MgO substrates by an ambient pressure chemical vapour deposition (CVD) method. We address the surface instability issue of the polar oxides which is the most challenging factor in MgO. Atomic force microscopy (AFM) measurements showed the topographical features of the graphene coated on MgO. X-ray photoelectron spectroscopy (XPS) study is carried out to extract information regarding the presence of necessary elements, their bonding with substrates and to confirm the sp-2 hybridization of carbon, which is a characteristic feature of graphene film. The chemical shift is due to the surface reconstruction of MgO in the prepared samples. For graphene-MgO interface, valence band offset (VBO) and conduction band offset (CBO) extracted from valence band spectra reported. Further, we predicted the energy band diagram for single layer and thin film of graphene. By using the room-temperature energy band gap values of MgO and graphene, the CBO is calculated to be 6.85 eV for single layer and 5.66 eV for few layer (1-3) of graphene layers.

  13. Impact of band structure and transition matrix elements on polarization properties of the photoluminescence of semipolar and nonpolar InGaN quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Schade, L.; Schwarz, U.T. [Department of Microsystems Engineering, University of Freiburg, Georges-Koehler-Allee 103, 79108 Freiburg (Germany); Fraunhofer Institute for Applied Solid State Physics (IAF), Tullastrasse 72, 79108 Freiburg (Germany); Wernicke, T. [Institute of Solid State Physics, Technical University, Hardenbergstrasse 36, 10623 Berlin (Germany); Weyers, M. [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany); Kneissl, M. [Institute of Solid State Physics, Technical University, Hardenbergstrasse 36, 10623 Berlin (Germany); Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany)

    2011-03-15

    Partial or full linear polarization is characteristic for the spontaneous emission of light from semipolar and nonpolar InGaN quantum wells. This property is an implication of the crystalline anisotropy as a basic property of the wurtzite structure. The influence of this anisotropy on the band structure and the transition matrix elements was calculated by a k.p-method for arbitrary quantum well orientations with respect to the c-axis; results are shown here in detail. Optical polarization is a direct consequence of a broken symmetry, mainly affecting the transition matrix elements from the conduction to the valence bands. Furthermore, the strain of the InGaN quantum well strongly depends on the crystal orientation of the substrate, resulting in a valence band mixing. The composition of the eigenfunctions has emerged to be most important for the polarization dependence of strained semipolar and nonpolar InGaN QW. The matrix elements, in combination with the thermal occupation of the bands, determine the polarization of the spontaneously emitted light. Our photoluminescence measurements of nonpolar QW match well with this model. However, in contrast to calculations with standard band parameters, the two topmost subbands show a larger separation in the emitted energy. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  14. 40 CFR 13.21 - Employee salary offset-general.

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 1 2010-07-01 2010-07-01 false Employee salary offset-general. 13.21... STANDARDS Administrative Offset § 13.21 Employee salary offset—general. (a) Purpose. This section... collection by salary offset under 5 U.S.C. 5514 of debts owed EPA and debts owed to other Federal agencies by...

  15. 45 CFR 708.10 - Procedures for salary offset.

    Science.gov (United States)

    2010-10-01

    ... 45 Public Welfare 3 2010-10-01 2010-10-01 false Procedures for salary offset. 708.10 Section 708... COLLECTION BY SALARY OFFSET FROM INDEBTED CURRENT AND FORMER EMPLOYEES § 708.10 Procedures for salary offset... to final salary payment, retired pay, or lump sum leave, etc. as of the date of separation to the...

  16. Economic and ecological outcomes of flexible biodiversity offset systems.

    Science.gov (United States)

    Habib, Thomas J; Farr, Daniel R; Schneider, Richard R; Boutin, Stan

    2013-12-01

    The commonly expressed goal of biodiversity offsets is to achieve no net loss of specific biological features affected by development. However, strict equivalency requirements may complicate trading of offset credits, increase costs due to restricted offset placement options, and force offset activities to focus on features that may not represent regional conservation priorities. Using the oil sands industry of Alberta, Canada, as a case study, we evaluated the economic and ecological performance of alternative offset systems targeting either ecologically equivalent areas (vegetation types) or regional conservation priorities (caribou and the Dry Mixedwood natural subregion). Exchanging dissimilar biodiversity elements requires assessment via a generalized metric; we used an empirically derived index of biodiversity intactness to link offsets with losses incurred by development. We considered 2 offset activities: land protection, with costs estimated as the net present value of profits of petroleum and timber resources to be paid as compensation to resource tenure holders, and restoration of anthropogenic footprint, with costs estimated from existing restoration projects. We used the spatial optimization tool MARXAN to develop hypothetical offset networks that met either the equivalent-vegetation or conservation-priority targets. Networks that required offsetting equivalent vegetation cost 2-17 times more than priority-focused networks. This finding calls into question the prudence of equivalency-based systems, particularly in relatively undeveloped jurisdictions, where conservation focuses on limiting and directing future losses. Priority-focused offsets may offer benefits to industry and environmental stakeholders by allowing for lower-cost conservation of valued ecological features and may invite discussion on what land-use trade-offs are acceptable when trading biodiversity via offsets. Resultados Económicos y Ecológicos de Sistemas de Compensación de

  17. Developmental Reversals in False Memory: Effects of Emotional Valence and Arousal

    Science.gov (United States)

    Brainerd, C. J.; Holliday, R. E.; Reyna, V. F.; Yang, Y.; Toglia, M. P.

    2010-01-01

    Do the emotional valence and arousal of events distort children's memories? Do valence and arousal modulate counterintuitive age increases in false memory? We investigated those questions in children, adolescents, and adults using the Cornell/Cortland Emotion Lists, a word list pool that induces false memories and in which valence and arousal can…

  18. Direct imaging of band profile in single layer MoS2 on graphite: quasiparticle energy gap, metallic edge states, and edge band bending.

    Science.gov (United States)

    Zhang, Chendong; Johnson, Amber; Hsu, Chang-Lung; Li, Lain-Jong; Shih, Chih-Kang

    2014-05-14

    Using scanning tunneling microscopy and spectroscopy, we probe the electronic structures of single layer MoS2 on graphite. The apparent quasiparticle energy gap of single layer MoS2 is measured to be 2.15 ± 0.06 eV at 77 K, albeit a higher second conduction band threshold at 0.2 eV above the apparent conduction band minimum is also observed. Combining it with photoluminescence studies, we deduce an exciton binding energy of 0.22 ± 0.1 eV (or 0.42 eV if the second threshold is use), a value that is lower than current theoretical predictions. Consistent with theoretical predictions, we directly observe metallic edge states of single layer MoS2. In the bulk region of MoS2, the Fermi level is located at 1.8 eV above the valence band maximum, possibly due to the formation of a graphite/MoS2 heterojunction. At the edge, however, we observe an upward band bending of 0.6 eV within a short depletion length of about 5 nm, analogous to the phenomena of Fermi level pinning of a 3D semiconductor by metallic surface states.

  19. Two-color infrared detector

    Science.gov (United States)

    Klem, John F; Kim, Jin K

    2014-05-13

    A two-color detector includes a first absorber layer. The first absorber layer exhibits a first valence band energy characterized by a first valence band energy function. A barrier layer adjoins the first absorber layer at a first interface. The barrier layer exhibits a second valence band energy characterized by a second valence band energy function. The barrier layer also adjoins a second absorber layer at a second interface. The second absorber layer exhibits a third valence band energy characterized by a third valence band energy function. The first and second valence band energy functions are substantially functionally or physically continuous at the first interface and the second and third valence band energy functions are substantially functionally or physically continuous at the second interface.

  20. Bond-Valence Constraints on Liquid Water Structure

    International Nuclear Information System (INIS)

    Bickmore, Barry R.; Rosso, Kevin M.; Brown, I. David; Kerisit, Sebastien N.

    2009-01-01

    The recent controversy about the structure of liquid water pits a new model involving water molecules in relatively stable rings-and-chains structures against the standard model that posits water molecules in distorted tetrahedral coordination. Molecular dynamics (MD) simulations 'both classical and ab initio' almost uniformly support the standard model, but since none of them can yet reproduce all the anomalous properties of water, they leave room for doubt. We argue that it is possible to evaluate these simulations by testing them against their adherence to the bond-valence model, a well known, and quantitatively accurate, empirical summary of the behavior of atoms in the bonded networks of inorganic solids. Here we use the results of ab initio molecular dynamics simulations of ice, water, and several solvated aqueous species to show that the valence sum rule (the first axiom of the bond-valence model,) is followed in both solid and liquid bond networks. We then test MD simulations of water, employing several popular potential models, against this criterion and the experimental O-O radial distribution function. It appears that most of those tested cannot satisfy both criteria well, except TIP4P and TIP5P. If the valence sum rule really can be applied to simulated liquid structures, then it follows that the bonding behaviors of atoms in liquids are in some ways identical to those in solids. We support this interpretation by showing that the simulations produce O-H-O geometries completely consistent with the range of geometries available in solids, and the distributions of instantaneous valence sums reaching the atoms in both the ice and liquid water simulations are essentially identical. Taken together, this is powerful evidence in favor of the standard distorted tetrahedral model of liquid water structure

  1. Common-image gathers in the offset domain from reverse-time migration

    KAUST Repository

    Zhan, Ge

    2014-04-01

    Kirchhoff migration is flexible to output common-image gathers (CIGs) in the offset domain by imaging data with different offsets separately. These CIGs supply important information for velocity model updates and amplitude-variation-with-offset (AVO) analysis. Reverse-time migration (RTM) offers more insights into complex geology than Kirchhoff migration by accurately describing wave propagation using the two-way wave equation. But, it has difficulty to produce offset domain CIGs like Kirchhoff migration. In this paper, we develop a method for obtaining offset domain CIGs from RTM. The method first computes the RTM operator of an offset gather, followed by a dot product of the operator and the offset data to form a common-offset RTM image. The offset domain CIGs are then achieved after separately migrating data with different offsets. We generate offset domain CIGs on both the Marmousi synthetic data and 2D Gulf of Mexico real data using this approach. © 2014.

  2. 19.2% Efficient InP Heterojunction Solar Cell with Electron-Selective TiO2 Contact.

    Science.gov (United States)

    Yin, Xingtian; Battaglia, Corsin; Lin, Yongjing; Chen, Kevin; Hettick, Mark; Zheng, Maxwell; Chen, Cheng-Ying; Kiriya, Daisuke; Javey, Ali

    2014-12-17

    We demonstrate an InP heterojunction solar cell employing an ultrathin layer (∼10 nm) of amorphous TiO 2 deposited at 120 °C by atomic layer deposition as the transparent electron-selective contact. The TiO 2 film selectively extracts minority electrons from the conduction band of p-type InP while blocking the majority holes due to the large valence band offset, enabling a high maximum open-circuit voltage of 785 mV. A hydrogen plasma treatment of the InP surface drastically improves the long-wavelength response of the device, resulting in a high short-circuit current density of 30.5 mA/cm 2 and a high power conversion efficiency of 19.2%.

  3. Optical properties of single wurtzite/zinc-blende ZnSe nanowires grown at low temperature

    Energy Technology Data Exchange (ETDEWEB)

    Zannier, V. [IOM-CNR Laboratorio TASC, S. S. 14, Km. 163.5, I-34149 Trieste (Italy); Department of Physics, University of Trieste, Via Valerio 2, I-34127 Trieste (Italy); Cremel, T.; Kheng, K. [Univ. Grenoble Alpes, F-38000 Grenoble (France); CEA, INAC-SP2M, « Nanophysique et Semiconducteurs » Group, F-38000 Grenoble (France); Artioli, A.; Ferrand, D. [Univ. Grenoble Alpes, F-38000 Grenoble (France); CNRS, Institut Néel, « Nanophysique et Semiconducteurs » Group, F-38000 Grenoble (France); Grillo, V. [IMEM-CNR, Parco Area delle Scienze 37/A, I-43010 Parma (Italy); S3 NANO-CNR, Via Campi 213/A, I-41125 Modena (Italy); Rubini, S. [IOM-CNR Laboratorio TASC, S. S. 14, Km. 163.5, I-34149 Trieste (Italy)

    2015-09-07

    ZnSe nanowires with a dominant wurtzite structure have been grown at low temperature (300 °C) by molecular beam epitaxy assisted by solid Au nanoparticles. The nanowires emission is polarized perpendicularly to their axis in agreement with the wurtzite selection rules. Alternations of wurtzite and zinc-blende regions have been observed by transmission electron microscopy, and their impact on the nanowires optical properties has been studied by microphotoluminescence. The nanowires show a dominant intense near-band-edge emission as well as the ZnSe wurtzite free exciton line. A type II band alignment between zinc-blende and wurtzite ZnSe is evidenced by time-resolved photoluminescence. From this measurement, we deduce values for the conduction and valence band offsets of 98 and 50 meV, respectively.

  4. Synchrotron Studies of Narrow Band and Low-Dimensional Materials. Final Report for July 1, 1990 --- December 31, 2002

    International Nuclear Information System (INIS)

    Allen, J. W.

    2003-01-01

    This report summarizes a 12-year program of various kinds of synchrotron spectroscopies directed at the electronic structures of narrow band and low-dimensional materials that display correlated electron behaviors such as metal-insulator transitions, mixed valence, superconductivity, Kondo moment quenching, heavy Fermions, and non-Fermi liquid properties

  5. Pressure-induced valence change and moderate heavy fermion state in Eu-compounds

    Science.gov (United States)

    Honda, Fuminori; Okauchi, Keigo; Sato, Yoshiki; Nakamura, Ai; Akamine, Hiromu; Ashitomi, Yosuke; Hedo, Masato; Nakama, Takao; Takeuchi, Tetsuya; Valenta, Jaroslav; Prchal, Jiri; Sechovský, Vladimir; Aoki, Dai; Ōnuki, Yoshichika

    2018-05-01

    A pressure-induced valence transition has attracted much attention in Eu-compounds. Among them, EuRh2Si2, EuNi2Ge2, and EuCo2Ge2 reveal the valence transition around 1, 2, and 3 GPa, respectively. We have succeeded in growing single crystals of EuT2X2 (T: transition metal, X: Si, Ge) and studied electronic properties under pressure. EuRh2Si2 indicates a first-order valence transition between 1 and 2 GPa, with a large and prominent hysteresis in the electrical resistivity. At higher pressures, the first-order valence transition changes to a cross-over regime with an intermediate valence state. Tuning of the valence state with pressure is reflected in a drastic change of the temperature dependence of the electrical resistivity in EuRh2Si2 single crystals. Effect of pressure on the valence states on EuRh2Si2, EuIr2Si2, EuNi2Ge2, and EuCo2Ge2, as well as an isostructural related compound EuGa4, are reviewed.

  6. DFT-based offset-QAM OFDM for optical communications.

    Science.gov (United States)

    Zhao, Jian

    2014-01-13

    We experimentally demonstrate and numerically investigate a discrete-Fourier-transform (DFT) based offset quadrature-amplitude-modulation (offset-QAM) orthogonal frequency division multiplexing (OFDM) system. We investigate the scheme using a set of square-root-raised-cosine functions and a set of super-Gaussian functions as signal spectra. It is shown that offset-QAM OFDM exhibits negligible penalty for all investigated spectra, in contrast to rectangular-function based Nyquist FDM (N-FDM) and sinc-function based conventional OFDM (C-OFDM). The required guard interval (GI) length for dispersion compensation in offset-QAM OFDM is analyzed and shown to scale with twice the subcarrier spacing rather than the full OFDM bandwidth. Experimental results show that 38-Gb/s offset-16QAM OFDM supports 600-km fiber transmission with negligible penalty in the absence of GI while a GI length of eight is required in C-OFDM. Further numerical simulations show that by avoiding the GI, 112-Gb/s polarization multiplexed offset-4QAM OFDM can achieve 23% increase in net data rate over C-OFDM under the same transmission reach. We also discuss the design of the pulse-shaping filter in the DFT-based implementation and show that when compared to N-FDM, the required memory length of the filter for pulse shaping can be reduced from 60 to 2 in offset-QAM OFDM regardless of the fiber length.

  7. Plutonium valence state distributions

    International Nuclear Information System (INIS)

    Silver, G.L.

    1974-01-01

    A calculational method for ascertaining equilibrium valence state distributions of plutonium in acid solutions as a function of the plutonium oxidation number and the solution acidity is illustrated with an example. The method may be more practical for manual use than methods based upon polynomial equations. (T.G.)

  8. CzEngVallex: a Bilingual Czech-English Valency Lexicon

    Directory of Open Access Journals (Sweden)

    Urešová Zdeňka

    2016-04-01

    Full Text Available This paper introduces a new bilingual Czech-English verbal valency lexicon (called CzEng-Vallex representing a relatively large empirical database. It includes 20,835 aligned valency frame pairs (i.e., verb senses which are translations of each other and their aligned arguments. This new lexicon uses data from the Prague Czech-English Dependency Treebank and also takes advantage of the existing valency lexicons for both languages: the PDT-Vallex for Czech and the EngVallex for English. The CzEngVallex is available for browsing as well as for download in the LINDAT/CLARIN repository.

  9. Band engineering in twisted molybdenum disulfide bilayers

    Science.gov (United States)

    Zhao, Yipeng; Liao, Chengwei; Ouyang, Gang

    2018-05-01

    In order to explore the theoretical relationship between interlayer spacing, interaction and band offset at the atomic level in vertically stacked two-dimensional (2D) van der Waals (vdW) structures, we propose an analytical model to address the evolution of interlayer vdW coupling with random stacking configurations in MoS2 bilayers based on the atomic-bond-relaxation correlation mechanism. We found that interlayer spacing changes substantially with respect to the orientations, and the bandgap increases from 1.53 eV (AB stacking) to 1.68 eV (AA stacking). Our results reveal that the evolution of interlayer vdW coupling originates from the interlayer interaction, leading to interlayer separations and electronic properties changing with stacking configurations. Our predictions constitute a demonstration of twist engineering the band shift in the emergent class of 2D crystals, transition-metal dichalcogenides.

  10. Surface potential, charging and local current transport of individual Ge quantum dots grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Singha, R.K. [Department of Physics, Visva-Bharati, Santiniketan 731235 (India); Manna, S.; Bar, R.; Das, S. [Department of Physics, Indian Institute of Technology-Kharagpur, Kharagpur 721302 (India); Ray, S.K., E-mail: physkr@phy.iitkgp.ernet.in [Department of Physics, Indian Institute of Technology-Kharagpur, Kharagpur 721302 (India)

    2017-06-15

    Highlights: We have elaborately explained the individual Ge QD charging phenomena and current transport, which is very important to understand the Ge/Si nano devices. This paper will give a flavor to properly understand these phenomena linked together along with the photocurrent mechanism which is related to the Ge/Si valence band offset. • Both the CAFM and KPFM techniques point out the functionality of doping nature of the underneath Si substrate on the aforementioned characteristics of Ge QDs. • Analysis of the surface potential mapping using KPFM technique yields an approximate valence band offset measurement which is required to understand the intra-valence transition of holes for the realization of long wavelength infrared photodetector. • KPFM and CAFM can be utilized to explore the charging/discharging phenomena of dots and their composition variations. • Current-voltage (I–V) characteristics of the individual Ge QD strongly depends on the individual QD size. • Energy band diagrams for diamond tip and Ge QD shows the higher barrier for electrons and lower barrier for holes allowing the easy tunneling for holes to dominate the transport. - Abstract: It is fundamentally important to understand the nanoscale electronic properties of a single quantum dot (QD) contrary to an ensemble of QDs. Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (CAFM) are two important tools, which could be employed to probe surface potential, charging phenomena, and current transport mechanism of individual QD. We demonstrate the aforementioned characteristics of self-assembled Ge QDs, which was grown on Si substrates by solid source molecular beam epitaxy driven by the Stranski-Krastanov method. Study reveals that each Ge QD acts as charge storage node even at zero applied bias. The shape, size and density of QDs could be well probed by CAFM and KPFM, whereas QD facets could be better resolved by the conductive tip. The CAFM investigation

  11. Carbon offset potentials and design: Anticipating future public policy

    International Nuclear Information System (INIS)

    Trexler, M.C.; Kosloff, L.H.; Gowen, M.

    1994-01-01

    Carbon offsets offer CO 2 emitters the opportunity to compensate for some proportion of their CO 2 emissions through the pursuit of emissions reduction or carbon sequestration projects beyond their own operational boundaries. The flexibility to pursue carbon offsets ''off-site'' can dramatically reduce the costs of achieving a given net emissions reduction. The future role of carbon offsets, however, continues to be a topic of considerable debate. Several processes are currently under way nationally and internationally that will help shape this role. This paper discusses how alternative policy outcomes could encourage or restrict the viability of carbon offsets as a component of corporate climate change mitigation portfolios and proposes criteria by which projects should be evaluated prior to the finalization of national or international policy frameworks. Based on these outcomes, the potential for offsets could be very large or very modest. It is vital that policy development in the offset arena account for the still voluntary nature of mitigation efforts and that the objective of climate change mitigation not be forgotten in the push for offset rules and regulations. At the same time, carbon offsets are far from a panacea for climate change mitigation and should be evaluated in the context of a larger global mitigation portfolio

  12. The quasiparticle band structure of zincblende and rocksalt ZnO.

    Science.gov (United States)

    Dixit, H; Saniz, R; Lamoen, D; Partoens, B

    2010-03-31

    We present the quasiparticle band structure of ZnO in its zincblende (ZB) and rocksalt (RS) phases at the Γ point, calculated within the GW approximation. The effect of the p-d hybridization on the quasiparticle corrections to the band gap is discussed. We compare three systems, ZB-ZnO which shows strong p-d hybridization and has a direct band gap, RS-ZnO which is also hybridized but includes inversion symmetry and therefore has an indirect band gap, and ZB-ZnS which shows a weaker hybridization due to a change of the chemical species from oxygen to sulfur. The quasiparticle corrections are calculated with different numbers of valence electrons in the Zn pseudopotential. We find that the Zn(20+) pseudopotential is essential for the adequate treatment of the exchange interaction in the self-energy. The calculated GW band gaps are 2.47 eV and 4.27 eV respectively, for the ZB and RS phases. The ZB-ZnO band gap is underestimated compared to the experimental value of 3.27 by ∼ 0.8 eV. The RS-ZnO band gap compares well with the experimental value of 4.5 eV. The underestimation for ZB-ZnO is correlated with the strong p-d hybridization. The GW band gap for ZnS is 3.57 eV, compared to the experimental value of 3.8 eV.

  13. THE VALENCE OF CORPUSCULAR PROTEINS.

    Science.gov (United States)

    Gorin, M H; Mover, L S

    1942-07-20

    BY THE USE OF TWO EXTREME MODELS: a hydrated sphere and an unhydrated rod the valence (net charge) of corpuscular proteins can be successfully calculated from electric mobility data by the Debye-Hückel theory (modified to include the effect of the ions in the ion atmosphere) in conjunction with the electrophoretic theory of Henry. As pointed out by Abramson, this permits a comparison with values for the valence from titration data. Electrometric titration measurements of serum albumin B (Kekwick) have been determined at several ionic strengths. These results, together with the available data in the literature for serum albumin B, egg albumin, and beta-lactoglobulin have been used to compare values for the valence calculated from measurements of titration, electrophoresis, and membrane potentials. The results indicate that the usual interpretation of titration curves is open to serious question. By extrapolation of the titration data to zero ionic strength and protein concentration, there results an "intrinsic" net charge curve describing the binding of H(+) (OH(-)) ion alone. This curve agrees closely, in each case, with values of the valence calculated from mobility data (which in turn are in close accord with those estimated from membrane potential measurements). The experimental titration curves in the presence of appreciable quantities of ions and protein deviate widely from the ideal curve. It is suggested that, under these conditions, binding of undissociated acid (base) leads to erroneous values for the net charge. This binding would not affect the electrophoretic mobility. Values of the net charge obtained by the two extreme models from electrophoretic data are in agreement within 15 to 20 per cent. The agreement between the cylindrical model and the titration data is somewhat better in each case than with the sphere; i.e., this comparison enables a choice to be made between asymmetry and hydration in the interpretation of results from sedimentation and

  14. Biodiversity offsets and the challenge of achieving no net loss.

    Science.gov (United States)

    Gardner, Toby A; VON Hase, Amrei; Brownlie, Susie; Ekstrom, Jonathan M M; Pilgrim, John D; Savy, Conrad E; Stephens, R T Theo; Treweek, Jo; Ussher, Graham T; Ward, Gerri; Ten Kate, Kerry

    2013-12-01

    Businesses, governments, and financial institutions are increasingly adopting a policy of no net loss of biodiversity for development activities. The goal of no net loss is intended to help relieve tension between conservation and development by enabling economic gains to be achieved without concomitant biodiversity losses. biodiversity offsets represent a necessary component of a much broader mitigation strategy for achieving no net loss following prior application of avoidance, minimization, and remediation measures. However, doubts have been raised about the appropriate use of biodiversity offsets. We examined what no net loss means as a desirable conservation outcome and reviewed the conditions that determine whether, and under what circumstances, biodiversity offsets can help achieve such a goal. We propose a conceptual framework to substitute the often ad hoc approaches evident in many biodiversity offset initiatives. The relevance of biodiversity offsets to no net loss rests on 2 fundamental premises. First, offsets are rarely adequate for achieving no net loss of biodiversity alone. Second, some development effects may be too difficult or risky, or even impossible, to offset. To help to deliver no net loss through biodiversity offsets, biodiversity gains must be comparable to losses, be in addition to conservation gains that may have occurred in absence of the offset, and be lasting and protected from risk of failure. Adherence to these conditions requires consideration of the wider landscape context of development and offset activities, timing of offset delivery, measurement of biodiversity, accounting procedures and rule sets used to calculate biodiversity losses and gains and guide offset design, and approaches to managing risk. Adoption of this framework will strengthen the potential for offsets to provide an ecologically defensible mechanism that can help reconcile conservation and development. Balances de Biodiversidad y el Reto de No Obtener P

  15. How economic contexts shape calculations of yield in biodiversity offsetting.

    Science.gov (United States)

    Carver, L; Sullivan, S

    2017-10-01

    We examined and analyzed methods used to create numerical equivalence between sites affected by development and proposed conservation offset sites. Application of biodiversity offsetting metrics in development impact and mitigation assessments is thought to standardize biodiversity conservation outcomes, sometimes termed yield by those conducting these calculations. The youth of biodiversity offsetting in application, however, means little is known about how biodiversity valuations and offset contracts between development and offset sites are agreed on in practice or about long-term conservation outcomes. We examined how sites were made commensurable and how biodiversity gains or yields were calculated and negotiated for a specific offset contract in a government-led pilot study of biodiversity offsets in England. Over 24 months, we conducted participant observations of various stages in the negotiation of offset contracts through repeated visits to 3 (anonymized) biodiversity offset contract sites. We conducted 50 semistructured interviews of stakeholders in regional and local government, the private sector, and civil society. We used a qualitative data analysis software program (DEDOOSE) to textually analyze interview transcriptions. We also compared successive iterations of biodiversity-offsetting calculation spreadsheets and planning documents. A particular focus was the different iterations of a specific biodiversity impact assessment in which the biodiversity offsetting metric developed by the U.K.'s Department for Environment, Food and Rural Affairs was used. We highlight 3 main findings. First, biodiversity offsetting metrics were amended in creative ways as users adapted inputs to metric calculations to balance and negotiate conflicting requirements. Second, the practice of making different habitats equivalent to each other through the application of biodiversity offsetting metrics resulted in commensuration outcomes that may not provide projected

  16. 5 CFR 179.213 - Coordinating salary offset with other agencies.

    Science.gov (United States)

    2010-01-01

    ... 5 Administrative Personnel 1 2010-01-01 2010-01-01 false Coordinating salary offset with other... REGULATIONS CLAIMS COLLECTION STANDARDS Salary Offset § 179.213 Coordinating salary offset with other agencies... intent of this regulation. (2) The designated salary offset coordinator will be responsible for: (i...

  17. The Effect of Allowing Pollution Offsets with Imperfect Enforcement

    OpenAIRE

    Hilary Sigman; Howard F. Chang

    2011-01-01

    Public policies for pollution control, including climate change policies, sometimes allow polluters in one sector subject to an emissions cap to offset excessive emissions in that sector with pollution abatement in another sector. The government may often find it more costly to verify offset claims than to verify compliance with emissions caps. Concerns about such difficulties in enforcement may lead regulators to restrict the use of offsets. In this paper, we demonstrate that allowing offset...

  18. Valence fluctuations between two magnetic configurations

    International Nuclear Information System (INIS)

    Mazzaferro, J.O.

    1982-01-01

    The subject of this work is the study of a microscopic model which describes TmSe through its most important feature, i.e.: the valence fluctuations between two magnetic configurations. Chapter I is a general review of the most important physical properties of rare-earth systems with intermediate valence (I.V.) and a general description of experimental results and theoretical models on Tm compounds. In Chapter II the Hamiltonian model is discussed and the loss of rotational invariance is also analyzed. Chapter III is devoted to the study of non-stoichiometric Tsub(x)Se compounds. It is shown that these compounds can be considered as a mixture of TmSe (I.V. system) and Tm 3+ 0.87Se. Chapter IV is devoted to the calculation of spin-and charge susceptibilities. The results obtained permit to explain the essential features of the neutron scattering spectrum in TmSe. In Chapter V, an exactly solvable periodic Hamiltonian is presented. From the experimental results, some fundamental features are deduced to describe TmSe as an intermediate valence system whose two accessible ionic configurations are magnetic (degenerated fundamental state). (M.E.L) [es

  19. Lying about the valence of affective pictures: an fMRI study.

    Directory of Open Access Journals (Sweden)

    Tatia M C Lee

    Full Text Available The neural correlates of lying about affective information were studied using a functional magnetic resonance imaging (fMRI methodology. Specifically, 13 healthy right-handed Chinese men were instructed to lie about the valence, positive or negative, of pictures selected from the International Affective Picture System (IAPS while their brain activity was scanned by a 3T Philip Achieva scanner. The key finding is that the neural activity associated with deception is valence-related. Comparing to telling the truth, deception about the valence of the affectively positive pictures was associated with activity in the inferior frontal, cingulate, inferior parietal, precuneus, and middle temporal regions. Lying about the valence of the affectively negative pictures, on the other hand, was associated with activity in the orbital and medial frontal regions. While a clear valence-related effect on deception was observed, common neural regions were also recruited for the process of deception about the valence of the affective pictures. These regions included the lateral prefrontal and inferior parietal regions. Activity in these regions has been widely reported in fMRI studies on deception using affectively-neutral stimuli. The findings of this study reveal the effect of valence on the neural activity associated with deception. Furthermore, the data also help to illustrate the complexity of the neural mechanisms underlying deception.

  20. 5th International Conference on Valence Fluctuations

    CERN Document Server

    Malik, S

    1987-01-01

    During the Koln meeting (August 28-31, 1984), Irdia was chosen as the venue for the next International Conference on Valence Fluctuations. lhis was in recognition ard appreciation of the work done, both experimental ard theoretical, by the Irdian scientists in this area during the last decade. We decided to hold this Conference in the month of January, 1987 at Bangalore. lhe subject of Valence Fluctuations has kept itself alive ard active as it has provided many shocks ard suprises particularly among the Ce- ard U-based intermetallies. lhe richness of many interesting physical phenomena occurring in mixed valent materials, the flexibility of modifying their physical properties (by alloying, for example) ard the possibility of synthesizing a wide variety of new such materials seem to be the key factors in this regard. Barely six months before this Conference, an International Conference on Anomalous Rare Earths and Actinides (ICAREA) had been held at Grenoble (July, 1986) which also focussed on mixed valence a...

  1. Evidence of ion intercalation mediated band structure modification and opto-ionic coupling in lithium niobite

    Science.gov (United States)

    Shank, Joshua C.; Tellekamp, M. Brooks; Doolittle, W. Alan

    2015-01-01

    The theoretically suggested band structure of the novel p-type semiconductor lithium niobite (LiNbO2), the direct coupling of photons to ion motion, and optically induced band structure modifications are investigated by temperature dependent photoluminescence. LiNbO2 has previously been used as a memristor material but is shown here to be useful as a sensor owing to the electrical, optical, and chemical ease of lithium removal and insertion. Despite the high concentration of vacancies present in lithium niobite due to the intentional removal of lithium atoms, strong photoluminescence spectra are observed even at room temperature that experimentally confirm the suggested band structure implying transitions from a flat conduction band to a degenerate valence band. Removal of small amounts of lithium significantly modifies the photoluminescence spectra including additional larger than stoichiometric-band gap features. Sufficient removal of lithium results in the elimination of the photoluminescence response supporting the predicted transition from a direct to indirect band gap semiconductor. In addition, non-thermal coupling between the incident laser and lithium ions is observed and results in modulation of the electrical impedance.

  2. Evidence of ion intercalation mediated band structure modification and opto-ionic coupling in lithium niobite

    International Nuclear Information System (INIS)

    Shank, Joshua C.; Tellekamp, M. Brooks; Doolittle, W. Alan

    2015-01-01

    The theoretically suggested band structure of the novel p-type semiconductor lithium niobite (LiNbO 2 ), the direct coupling of photons to ion motion, and optically induced band structure modifications are investigated by temperature dependent photoluminescence. LiNbO 2 has previously been used as a memristor material but is shown here to be useful as a sensor owing to the electrical, optical, and chemical ease of lithium removal and insertion. Despite the high concentration of vacancies present in lithium niobite due to the intentional removal of lithium atoms, strong photoluminescence spectra are observed even at room temperature that experimentally confirm the suggested band structure implying transitions from a flat conduction band to a degenerate valence band. Removal of small amounts of lithium significantly modifies the photoluminescence spectra including additional larger than stoichiometric-band gap features. Sufficient removal of lithium results in the elimination of the photoluminescence response supporting the predicted transition from a direct to indirect band gap semiconductor. In addition, non-thermal coupling between the incident laser and lithium ions is observed and results in modulation of the electrical impedance

  3. Valence electronic properties of porphyrin derivatives.

    Science.gov (United States)

    Stenuit, G; Castellarin-Cudia, C; Plekan, O; Feyer, V; Prince, K C; Goldoni, A; Umari, P

    2010-09-28

    We present a combined experimental and theoretical investigation of the valence electronic structure of porphyrin-derived molecules. The valence photoemission spectra of the free-base tetraphenylporphyrin and of the octaethylporphyrin molecule were measured using synchrotron radiation and compared with theoretical spectra calculated using the GW method and the density-functional method within the generalized gradient approximation. Only the GW results could reproduce the experimental data. We found that the contribution to the orbital energies due to electronic correlations has the same linear behavior in both molecules, with larger deviations in the vicinity of the HOMO level. This shows the importance of adequate treatment of electronic correlations in these organic systems.

  4. Offset Compound Gear Drive

    Science.gov (United States)

    Stevens, Mark A.; Handschuh, Robert F.; Lewicki, David G.

    2010-01-01

    The Offset Compound Gear Drive is an in-line, discrete, two-speed device utilizing a special offset compound gear that has both an internal tooth configuration on the input end and external tooth configuration on the output end, thus allowing it to mesh in series, simultaneously, with both a smaller external tooth input gear and a larger internal tooth output gear. This unique geometry and offset axis permits the compound gear to mesh with the smaller diameter input gear and the larger diameter output gear, both of which are on the same central, or primary, centerline. This configuration results in a compact in-line reduction gear set consisting of fewer gears and bearings than a conventional planetary gear train. Switching between the two output ratios is accomplished through a main control clutch and sprag. Power flow to the above is transmitted through concentric power paths. Low-speed operation is accomplished in two meshes. For the purpose of illustrating the low-speed output operation, the following example pitch diameters are given. A 5.0 pitch diameter (PD) input gear to 7.50 PD (internal tooth) intermediate gear (0.667 reduction mesh), and a 7.50 PD (external tooth) intermediate gear to a 10.00 PD output gear (0.750 reduction mesh). Note that it is not required that the intermediate gears on the offset axis be of the same diameter. For this example, the resultant low-speed ratio is 2:1 (output speed = 0.500; product of stage one 0.667 reduction and stage two 0.750 stage reduction). The design is not restricted to the example pitch diameters, or output ratio. From the output gear, power is transmitted through a hollow drive shaft, which, in turn, drives a sprag during which time the main clutch is disengaged.

  5. 12 CFR 313.49 - Coordinating salary offset with other agencies.

    Science.gov (United States)

    2010-01-01

    ... 12 Banks and Banking 4 2010-01-01 2010-01-01 false Coordinating salary offset with other agencies... PRACTICE PROCEDURES FOR CORPORATE DEBT COLLECTION Salary Offset § 313.49 Coordinating salary offset with... employee has consented to the salary offset in writing or has signed a statement acknowledging receipt of...

  6. Valence-to-core-detected X-ray absorption spectroscopy

    DEFF Research Database (Denmark)

    Hall, Eleanor R.; Pollock, Christopher J.; Bendix, Jesper

    2014-01-01

    X-ray absorption spectroscopy (XAS) can provide detailed insight into the electronic and geometric structures of transition-metal active sites in metalloproteins and chemical catalysts. However, standard XAS spectra inherently represent an average contribution from the entire coordination...... environment with limited ligand selectivity. To address this limitation, we have investigated the enhancement of XAS features using valence-to-core (VtC)-detected XAS, whereby XAS spectra are measured by monitoring fluorescence from valence-to-core X-ray emission (VtC XES) events. VtC emission corresponds...... to transitions from filled ligand orbitals to the metal 1s core hole, with distinct energetic shifts for ligands of differing ionization potentials. VtC-detected XAS data were obtained from multiple valence emission features for a series of well-characterized Mn model compounds; taken together, these data...

  7. Field-induced valence transition in rare-earth system

    International Nuclear Information System (INIS)

    Chattopadhaya, A.; Ghatak, S.K.

    2000-01-01

    The magnetic field-induced valence transition in rare-earth compound has been examined based on a pseudospin S=1 Ising model proposed earlier for valence transition. The model includes finite mixing between two pertinent ionic configurations (magnetic and non-magnetic) separated by an energy gap and with intersite interaction between rare-earth ions. Using the mean field approximation the magnetic behaviour and the critical field (H c ) for transition are obtained as a function of energy gap and temperature. The phase boundary defined in terms of reduced field H c /H co and reduced temperature T/T v (T v being valence transition temperature in absence of field) is nearly independent of energy gap. These results are in qualitative agreement with experimental observation in Yb- and Eu-compounds

  8. Work Valence as a Predictor of Academic Achievement in the Family Context

    Science.gov (United States)

    Porfeli, Erik; Ferrari, Lea; Nota, Laura

    2013-01-01

    This study asserts a theoretical model of academic and work socialization within the family setting. The presumed associations between parents' work valences, children's work valences and valence perceptions, and children's academic interest and achievement are tested. The results suggest that children's perceptions of parents mediate the…

  9. Quadrupole to BPM offset determination in Indus-2

    International Nuclear Information System (INIS)

    Jena, Saroj; Ghodke, A.D.; Singh, G.

    2009-01-01

    A feasibility of finding the quadrupole to BPM offset using beam based alignment (BBA) technique in Indus-2 has been studied. The measurements of the offsets between BPM and quadrupoles could be performed by using quadratic fitting for the minima of the orbit response w. r. t. changes in the quadrupole strengths. These offsets will be integrated to the orbit data during closed orbit correction. There are 72 quadrupoles and 56 BPMs in Indus-2. However the assessment of Quad-BPM offsets is not feasible in some cases due to non-availability of BPM adjacent to quadrupole and also in some cases because of a large phase advance between quadrupole and nearby BPM. Here single corrector method is used to obtain these offsets and assumed the current of each quadrupole can be varied independently. A graphical user interface (GUI) is developed in MATLAB for the use of BBA in Indus-2. (author)

  10. 15 CFR 19.10 - How will Commerce entities use administrative offset (offset of non-tax Federal payments) to...

    Science.gov (United States)

    2010-01-01

    ... 15 Commerce and Foreign Trade 1 2010-01-01 2010-01-01 false How will Commerce entities use administrative offset (offset of non-tax Federal payments) to collect a Commerce debt? 19.10 Section 19.10 Commerce and Foreign Trade Office of the Secretary of Commerce COMMERCE DEBT COLLECTION Procedures To...

  11. Actinides, the narrowwest bands

    International Nuclear Information System (INIS)

    Smith, J.L.; Riseborough, P.S.

    1984-01-01

    A table of elements is shown that demonstrates the crossover from superconductivity to magnetism as well as regions of mixed valence. In particular, the actinides must eventually show 4f-electron like mixed valence, after the 5f-electrons become localized. There also seems to be an adiabatic continuation between heavy fermion and mixed valence behavior

  12. Offset Trace-Based Video Quality Evaluation Network Transport

    DEFF Research Database (Denmark)

    Seeling, P.; Reisslein, M.; Fitzek, Frank

    2006-01-01

    Video traces contain information about encoded video frames, such as frame sizes and qualities, and provide a convenient method to conduct multimedia networking research. Although wiedely used in networking research, these traces do not allow to determine the video qaulityin an accurate manner...... after networking transport that includes losses and delays. In this work, we provide (i) an overview of frame dependencies that have to be taken into consideration when working with video traces, (ii) an algorithmic approach to combine traditional video traces and offset distortion traces to determine...... the video quality or distortion after lossy network transport, (iii) offset distortion and quality characteristics and (iv) the offset distortion trace format and tools to create offset distortion traces....

  13. Band-gap creation by icosahedral symmetry in nearly-free-electron materials

    International Nuclear Information System (INIS)

    Carlsson, A.E.

    1993-01-01

    A series of numerical electronic density-of-states calculations is performed for rational approximants to a model one-electron potential based on icosahedrally arranged plane-wave components. It is found that high-order approximants can have band gaps even if the low-order approximants do not; furthermore, the magnitude of the gap increases with the order of the approximant. The results are interpreted via a two- and three-wave analysis of the energy eigenvalues at the pseudo-Jones-zone faces and edges. It is also found that the mechanism of band-gap reduction in the rational approximants is the presence of a small density of gap states. An analytic calculation shows that these gap states result from a splitting of threefold and pseudothreefold states at the valence-band edge when the icosahedral symmetry is broken. The splitting is proportional to the error with which the ratio between the approximant indices approximates τ, the golden mean. Finally, an application to the AlCuLi system is presented

  14. A theoretical investigation of valence and Rydberg electronic states of acrolein

    International Nuclear Information System (INIS)

    Aquilante, Francesco; Barone, Vincenzo; Roos, Bjoern O.

    2003-01-01

    The main features of the ultraviolet spectrum of acrolein have been studied by a multireference perturbative treatment and by a time dependent density functional approach. The valence and Rydberg transition energies have been calculated and the assignment of the experimental bands has been clarified. The different relaxation trends of the three lowest singlet and triplet excited states have been analyzed by unconstrained geometry optimizations. This has allowed, in particular, the characterization of a twisted 3 (ππ*) state, which is crucial for the interesting photophysics and photochemistry of the acrolein molecule and, more generally, of the α,β-enones. Solvatochromic shifts in aqueous solution have been investigated using a combined discrete/continuum approach based on the so called polarizable continuum model. The experimental trends are well reproduced by this approach and a closer degeneracy in the triplet manifold has been detected in solution with respect to gas phase

  15. Phase Offsets and the Energy Budgets of Hot Jupiters

    Science.gov (United States)

    Schwartz, Joel C.; Kashner, Zane; Jovmir, Diana; Cowan, Nicolas B.

    2017-12-01

    Thermal phase curves of short-period planets on circular orbits provide joint constraints on the fraction of incoming energy that is reflected (Bond albedo) and the fraction of absorbed energy radiated by the night hemisphere (heat recirculation efficiency). Many empirical studies of hot Jupiters have implicitly assumed that the dayside is the hottest hemisphere and the nightside is the coldest hemisphere. For a given eclipse depth and phase amplitude, an orbital lag between a planet’s peak brightness and its eclipse—a phase offset—implies that planet’s nightside emits greater flux. To quantify how phase offsets impact the energy budgets of short-period planets, we compile all infrared observations of the nine planets with multi-band eclipse depths and phase curves. Accounting for phase offsets shifts planets to lower Bond albedo and greater day-night heat transport, usually by ≲1σ. For WASP-12b, the published phase variations have been analyzed in two different ways, and the inferred energy budget depends sensitively on which analysis one adopts. Our fiducial scenario supports a Bond albedo of {0.27}-0.13+0.12, significantly higher than the published optical geometric albedo, and a recirculation efficiency of {0.03}-0.02+0.07, following the trend of larger day-night temperature contrast with greater stellar irradiation. If instead we adopt the alternative analysis, then WASP-12b has a Bond albedo consistent with zero and a much higher recirculation efficiency. To definitively determine the energy budget of WASP-12b, new observational analyses will be necessary.

  16. Transition-metal impurities in semiconductors and heterojunction band lineups

    Science.gov (United States)

    Langer, Jerzy M.; Delerue, C.; Lannoo, M.; Heinrich, Helmut

    1988-10-01

    The validity of a recent proposal that transition-metal impurity levels in semiconductors may serve as a reference in band alignment in semiconductor heterojunctions is positively verified by using the most recent data on band offsets in the following lattice-matched heterojunctions: Ga1-xAlxAs/GaAs, In1-xGaxAsyP1-y/InP, In1-xGaxP/GaAs, and Cd1-xHgxTe/CdTe. The alignment procedure is justified theoretically by showing that transition-metal energy levels are effectively pinned to the average dangling-bond energy level, which serves as the reference level for the heterojunction band alignment. Experimental and theoretical arguments showing that an increasingly popular notion on transition-metal energy-level pinning to the vacuum level is unjustified and must be abandoned in favor of the internal-reference rule proposed recently [J. M. Langer and H. Heinrich, Phys. Rev. Lett. 55, 1414 (1985)] are presented.

  17. Creation of quasi-Dirac points in the Floquet band structure of bilayer graphene.

    Science.gov (United States)

    Cheung, W M; Chan, K S

    2017-06-01

    We study the Floquet quasi-energy band structure of bilayer graphene when it is illuminated by two laser lights with frequencies [Formula: see text] and [Formula: see text] using Floquet theory. We focus on the dynamical gap formed by the conduction band with Floquet index  =  -1 and the valence band with Floquet index  =  +1 to understand how Dirac points can be formed. It is found that the dynamical gap does not have rotation symmetry in the momentum space, and quasi-Dirac points, where the conduction and valence bands almost touch, can be created when the dynamical gap closes along some directions with suitably chosen radiation parameters. We derive analytical expressions for the direction dependence of the dynamical gaps using Lowdin perturbation theory to gain a better understanding of the formation of quasi-Dirac points. When both radiations are circularly polarized, the gap can be exactly zero along some directions, when only the first and second order perturbations are considered. Higher order perturbations can open a very small gap in this case. When both radiations are linearly polarized, the gap can be exactly zero up to the fourth order perturbation and more than one quasi-Dirac point is formed. We also study the electron velocity around a dynamical gap and show that the magnitude of the velocity drops to values close to zero when the k vector is near to the gap minimum. The direction of the velocity also changes around the gap minimum, and when the gap is larger in value the change in the velocity direction is more gradual. The warping effect does not affect the formation of a Dirac point along the k x axis, while it prevents its formation when there is phase shift between the two radiations.

  18. 10 CFR 16.15 - Procedures for internal salary offset.

    Science.gov (United States)

    2010-01-01

    ... 10 Energy 1 2010-01-01 2010-01-01 false Procedures for internal salary offset. 16.15 Section 16.15 Energy NUCLEAR REGULATORY COMMISSION SALARY OFFSET PROCEDURES FOR COLLECTING DEBTS OWED BY FEDERAL EMPLOYEES TO THE FEDERAL GOVERNMENT § 16.15 Procedures for internal salary offset. (a) Deductions to...

  19. Emotions and false memories: valence or arousal?

    Science.gov (United States)

    Corson, Yves; Verrier, Nadège

    2007-03-01

    The effects of mood on false memories have not been studied systematically until recently. Some results seem to indicate that negative mood may reduce false recall and thus suggest an influence of emotional valence on false memory. The present research tested the effects of both valence and arousal on recall and recognition and indicates that the effect is actually due to arousal. In fact, whether participants' mood is positive, negative, or neutral, false memories are significantly more frequent under conditions of high arousal than under conditions of low arousal.

  20. Excitations of one-valence-proton, one-valence-neutron nucleus {sup 210}Bi from cold-neutron capture

    Energy Technology Data Exchange (ETDEWEB)

    Cieplicka-Oryńczak, N. [INFN sezione di Milano, Via Celoria 16, 20133 Milano (Italy); Institute of Nuclear Physics, Polish Academy of Sciences, PL-31342 Kraków (Poland); Fornal, B.; Szpak, B. [Institute of Nuclear Physics, Polish Academy of Sciences, PL-31342 Kraków (Poland); Leoni, S.; Bottoni, S. [INFN sezione di Milano, Via Celoria 16, 20133 Milano (Italy); Università degli Studi di Milano, Via Celoria 16, 20133 Milano (Italy); Bazzacco, D. [Dipartimento di Fisica e Astronomia dell’Università, I-35131 Padova (Italy); INFN Sezione di Padova, I-35131 Padova (Italy); Blanc, A.; Jentschel, M.; Köster, U.; Mutti, P.; Soldner, T. [Institute Laue-Langevin, 6, rue Jules Horowitz, 38042 Grenoble Cedex 9 (France); Bocchi, G. [Università degli Studi di Milano, Via Celoria 16, 20133 Milano (Italy); France, G. de [GANIL, Bd. Becquerel, BP 55027, 14076 CAEN Cedex 05 (France); Simpson, G. [LPSC, Université Joseph Fourier Grenoble 1, CNRS/IN2P3, Institut National Polytechnique de Grenoble, F-38026 Grenoble Cedex (France); Ur, C. [INFN Sezione di Padova, Via F. Marzolo 8, I-35131 Padova (Italy); Urban, W. [Faculty of Physics, University of Warsaw, ul. Hoża 69, 02-681, Warszawa (Poland)

    2015-10-15

    The low-spin structure of one-proton, one-neutron {sup 210}Bi nucleus was investigated in cold-neutron capture reaction on {sup 209}Bi. The γ-coincidence measurements were performed with use of EXILL array consisted of 16 HPGe detectors. The experimental results were compared to shell-model calculations involving valence particles excitations. The {sup 210}Bi nucleus offers the potential to test the effective proton-neutron interactions because most of the states should arise from the proton-neutron excitations. Additionally, it was discovered that a few states should come from the couplings of valence particles to the 3{sup −} octupole vibration in {sup 208}Pb which provides also the possibility of testing the calculations involving the core excitations.

  1. Tunable Band Gap and Conductivity Type of ZnSe/Si Core-Shell Nanowire Heterostructures

    Directory of Open Access Journals (Sweden)

    Yijie Zeng

    2014-10-01

    Full Text Available The electronic properties of zincblende ZnSe/Si core-shell nanowires (NWs with a diameter of 1.1–2.8 nm are calculated by means of the first principle calculation. Band gaps of both ZnSe-core/Si-shell and Si-core/ZnSe-shell NWs are much smaller than those of pure ZnSe or Si NWs. Band alignment analysis reveals that the small band gaps of ZnSe/Si core-shell NWs are caused by the interface state. Fixing the ZnSe core size and enlarging the Si shell would turn the NWs from intrinsic to p-type, then to metallic. However, Fixing the Si core and enlarging the ZnSe shell would not change the band gap significantly. The partial charge distribution diagram shows that the conduction band maximum (CBM is confined in Si, while the valence band maximum (VBM is mainly distributed around the interface. Our findings also show that the band gap and conductivity type of ZnSe/Si core-shell NWs can be tuned by the concentration and diameter of the core-shell material, respectively.

  2. Valency state changes in lanthanide-contained systems under high pressure

    Energy Technology Data Exchange (ETDEWEB)

    Jayaraman, A

    1980-08-01

    Changes in valency state induced by pressure in samarium sulphide SmS remind one of alchemy, as the mat black initial substance shines golden after the electron transition. The alchemist's dream is of course not realized, however the compound does exhibit an unusually interesting behaviour in the new state. The valency state of samarium as newly appeared fluctuated very rapidly between two electron configurations. Manipulation of the valency state by pressure or chemical substitution can basically change the physical properties of systems containing lanthanides. The phenomena are described and discussed in the following survey.

  3. Assignment of Nilsson orbitals at superdeformation - identical bands

    Energy Technology Data Exchange (ETDEWEB)

    Ragnarsson, I [Lund Univ. (Sweden). Dept. of Mathematical Physics

    1992-08-01

    The relative transition energies of superdeformed rotational bands are used to extract ``effective alignments`` of the valence particles. It is found that the effective alignments give a direct picture of the Nilsson orbitals which are active in {sup 146-150}Gd, i.e., especially the orbitals [651 1/2] and [642 5/2], and that all bands observed in these nuclei can be understood within one consistent scheme. The experimental features are reproduced in calculations using the Nilsson-Strutinsky cranking model. The nearly identical transition energies seen in neighboring odd-proton and even-proton nuclei in the Dy/Tb/Gd region are investigated using the same formalism. Again, a consistent picture seems to emerge where, as suggested previously, the nucleus with a hole in the [301 1/2] Nilsson orbital and the corresponding core nucleus have calculated transition energies which are almost identical over a large range in spin. 2 refs., figs.

  4. Band structure and dielectric function of TlInTe2

    International Nuclear Information System (INIS)

    Wakita, K.; Shim, Y.; Orudzhev, G.; Mamedov, N.; Hashimzade, F.

    2006-01-01

    The band structure of ternary chain TlInTe 2 was calculated with allowance for non-locality of ionic pseudo-potentials. The dielectric function, as well as the effective masses of holes and electrons, the effective number of valence electrons, and the function of characteristic losses were determined. The results of comparison between the calculated dielectric function and the one obtained ellipsometrically in the spectral range from 0.85 to 6 eV are quite favorable. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (Abstract Copyright [2006], Wiley Periodicals, Inc.)

  5. Achieving biodiversity benefits with offsets: Research gaps, challenges, and needs.

    Science.gov (United States)

    Gelcich, Stefan; Vargas, Camila; Carreras, Maria Jose; Castilla, Juan Carlos; Donlan, C Josh

    2017-03-01

    Biodiversity offsets are becoming increasingly common across a portfolio of settings: national policy, voluntary programs, international lending, and corporate business structures. Given the diversity of ecological, political, and socio-economic systems where offsets may be applied, place-based information is likely to be most useful in designing and implementing offset programs, along with guiding principles that assure best practice. We reviewed the research on biodiversity offsets to explore gaps and needs. While the peer-reviewed literature on offsets is growing rapidly, it is heavily dominated by ecological theory, wetland ecosystems, and U.S.-based research. Given that majority of offset policies and programs are occurring in middle- and low-income countries, the research gaps we identified present a number of risks. They also present an opportunity to create regionally based learning platforms focused on pilot projects and institutional capacity building. Scientific research should diversify, both topically and geographically, in order to support the successful design, implementation, and monitoring of biodiversity offset programs.

  6. Multi-analysis and modeling of asymmetry offset for Hall effect structures

    Energy Technology Data Exchange (ETDEWEB)

    Paun, Maria-Alexandra, E-mail: maria_paun2003@yahoo.com

    2017-03-15

    The topological (asymmetry) offset voltage of CMOS cross-like Hall cells is analyzed in this paper. In order to attain the stated objective, different approaches have been considered. Both circuit and three-dimensional models have been developed. Variation of the misalignment offset with the biasing current has been studied through physical and circuit models. The latter is a non-homogenous finite elements model, which relies on using parameterized resistances and current-controlled current sources, of CMOS Hall cells. The displacement offset for various asymmetries and the offset variation with the temperature were investigated through the circuit model developed. Various experimental results for the single and magnetic equivalent offset have also been provided. - Highlights: • In this paper both physical and circuit models have been proposed for the evaluation of Hall cells offset. • Variation of the misalignment offset with the biasing current has been studied. • The displacement offset for various asymmetries and the offset variation with the temperature were investigated. • Various experimental results for single and magnetic equivalent offset were provided. • The obtained simulation results are in accordance with the experimental data.

  7. An intercomparison of the thermal offset for different pyranometers

    Science.gov (United States)

    Sanchez, G.; Cancillo, M. L.; Serrano, A.

    2016-07-01

    An unprecedented intensive intercomparison campaign focused on the experimental measurement of the thermal offset of pyranometers has been conducted at Badajoz (Spain) with the participation of three main manufacturers. The purpose of this study is to compare the thermal offset of six commercially available pyranometers, being some of them widely used and others recently commercialized. In this campaign, the capping methodology has been used to experimentally measure the daytime thermal offset of the pyranometers. Thus, a short but intense campaign has been conducted in two selected summer days under clear-sky conditions, covering a large range of solar zenith angle, irradiance, and temperature. Along the campaign, a total of 305 capping events have been performed, 61 for each pyranometer. The daytime thermal offset obtained for different pyranometers ranges between 0 and -16.8 W/m2 depending on the environmental conditions, being sometimes notably higher than values estimated indoors by manufacturers. The thermal offset absolute value of all instruments shows a diurnal cycle, increasing from sunrise to central hours of the day and decreasing from midafternoon to sunset. The analysis demonstrates that thermal offset is notably higher and more variable during daytime than during nighttime, requiring specific daytime measurements. Main results emphasize the key role played by wind speed in modulating the thermal offset.

  8. Light emitting diode based on n-Zn0.94M0.06O nanorods/p-GaN (M= Cd and Ni) heterojunction under forward and reverse bias

    International Nuclear Information System (INIS)

    Echresh, Ahmad; Oeurn Chey, Chan; Zargar Shoushtari, Morteza; Nur, Omer; Willander, Magnus

    2015-01-01

    In this study, we report on the improvement in the optoelectronic properties of n-ZnO nanorods/p-GaN heterojunction. This was achieved by doping the ZnO with cadmium (Cd) and nickel (Ni). The ZnO and Zn 0.94 M 0.06 O nanorods grown hydrothermally on the p-GaN substrate were used to fabricate the light emitting diodes (LEDs). Structural measurement revealed that nanorods with wurtzite structure having a preferential orientation along the (002) c-axis. The UV–vis spectra show that the optical band gap of Zn 0.94 M 0.06 O nanorods is decreased in comparison to ZnO nanorods. Electrical measurements of the fabricated LEDs show an obvious rectifying behaviour with low threshold voltage. Electroluminescence (EL) characteristics of LEDs operated at forward and reverse bias were investigated. The EL spectra under forward bias show that doping ZnO nanorods with Cd and Ni led to an intensity enhancement of the broad peak in the visible region while the blue peak originating from the p-GaN substrate remains almost unaffected. The effect of doping was to reduce the valence band offsets and consequently more hole injection has occurred leading to the observed enhancement of the broad band in the visible region. Under reverse bias all heterojunction LEDs show the blue light emission peak originating from the p-GaN substrate. - Highlights: • The reduction of the optical band gap of the M-doped ZnO (M= Cd and Ni) nanorods results in reduction of the valence band offset of the n-Zn 0.94 M 0.06 O nanorods/p-GaN heterojunction LEDs. • Doping ZnO nanorods with Cd and Ni led to an intensity enhancement of the broad peak in the visible region under forward bias. • Under reverse bias all heterojunction LEDs show the blue light emission peak originating from the p-GaN substrate

  9. Light emitting diode based on n-Zn{sub 0.94}M{sub 0.06}O nanorods/p-GaN (M= Cd and Ni) heterojunction under forward and reverse bias

    Energy Technology Data Exchange (ETDEWEB)

    Echresh, Ahmad, E-mail: ahmadechresh@gmail.com [Department of Science and Technology, Physical Electronics and Nanotechnology Division, Campus Norrköping, Linköping University (Sweden); Department of Physics, Shahid Chamran University of Ahvaz, Ahvaz (Iran, Islamic Republic of); Oeurn Chey, Chan [Department of Science and Technology, Physical Electronics and Nanotechnology Division, Campus Norrköping, Linköping University (Sweden); Zargar Shoushtari, Morteza [Department of Physics, Shahid Chamran University of Ahvaz, Ahvaz (Iran, Islamic Republic of); Nur, Omer; Willander, Magnus [Department of Science and Technology, Physical Electronics and Nanotechnology Division, Campus Norrköping, Linköping University (Sweden)

    2015-04-15

    In this study, we report on the improvement in the optoelectronic properties of n-ZnO nanorods/p-GaN heterojunction. This was achieved by doping the ZnO with cadmium (Cd) and nickel (Ni). The ZnO and Zn{sub 0.94}M{sub 0.06}O nanorods grown hydrothermally on the p-GaN substrate were used to fabricate the light emitting diodes (LEDs). Structural measurement revealed that nanorods with wurtzite structure having a preferential orientation along the (002) c-axis. The UV–vis spectra show that the optical band gap of Zn{sub 0.94}M{sub 0.06}O nanorods is decreased in comparison to ZnO nanorods. Electrical measurements of the fabricated LEDs show an obvious rectifying behaviour with low threshold voltage. Electroluminescence (EL) characteristics of LEDs operated at forward and reverse bias were investigated. The EL spectra under forward bias show that doping ZnO nanorods with Cd and Ni led to an intensity enhancement of the broad peak in the visible region while the blue peak originating from the p-GaN substrate remains almost unaffected. The effect of doping was to reduce the valence band offsets and consequently more hole injection has occurred leading to the observed enhancement of the broad band in the visible region. Under reverse bias all heterojunction LEDs show the blue light emission peak originating from the p-GaN substrate. - Highlights: • The reduction of the optical band gap of the M-doped ZnO (M= Cd and Ni) nanorods results in reduction of the valence band offset of the n-Zn{sub 0.94}M{sub 0.06}O nanorods/p-GaN heterojunction LEDs. • Doping ZnO nanorods with Cd and Ni led to an intensity enhancement of the broad peak in the visible region under forward bias. • Under reverse bias all heterojunction LEDs show the blue light emission peak originating from the p-GaN substrate.

  10. Topologically distinct classes of valence-bond solid states with their parent Hamiltonians

    International Nuclear Information System (INIS)

    Tu Honghao; Zhang Guangming; Xiang Tao; Liu Zhengxin; Ng Taikai

    2009-01-01

    We present a general method to construct one-dimensional translationally invariant valence-bond solid states with a built-in Lie group G and derive their matrix product representations. The general strategies to find their parent Hamiltonians are provided so that the valence-bond solid states are their unique ground states. For quantum integer-spin-S chains, we discuss two topologically distinct classes of valence-bond solid states: one consists of two virtual SU(2) spin-J variables in each site and another is formed by using two SO(2S+1) spinors. Among them, a spin-1 fermionic valence-bond solid state, its parent Hamiltonian, and its properties are discussed in detail. Moreover, two types of valence-bond solid states with SO(5) symmetries are further generalized and their respective properties are analyzed as well.

  11. Developmental Reversals in False Memory: Effects of Emotional Valence and Arousal

    OpenAIRE

    Brainerd, C. J.; Holliday, R. E.; Reyna, V. F.; Yang, Y.; Toglia, M. P.

    2010-01-01

    Do the emotional valence and arousal of events distort children’s memories? Do valence and arousal modulate counterintuitive age increases in false memory? We investigated those questions in children, adolescents, and adults using the Cornell/Cortland Emotion Lists, a word list pool that induces false memories and in which valence and arousal can be manipulated factorially. False memories increased with age for unpresented semantic associates of word lists, and net accuracy (the ratio of true...

  12. Tantalum Nitride Electron-Selective Contact for Crystalline Silicon Solar Cells

    KAUST Repository

    Yang, Xinbo

    2018-04-19

    Minimizing carrier recombination at contact regions by using carrier‐selective contact materials, instead of heavily doping the silicon, has attracted considerable attention for high‐efficiency, low‐cost crystalline silicon (c‐Si) solar cells. A novel electron‐selective, passivating contact for c‐Si solar cells is presented. Tantalum nitride (TaN x ) thin films deposited by atomic layer deposition are demonstrated to provide excellent electron‐transporting and hole‐blocking properties to the silicon surface, due to their small conduction band offset and large valence band offset. Thin TaNx interlayers provide moderate passivation of the silicon surfaces while simultaneously allowing a low contact resistivity to n‐type silicon. A power conversion efficiency (PCE) of over 20% is demonstrated with c‐Si solar cells featuring a simple full‐area electron‐selective TaNx contact, which significantly improves the fill factor and the open circuit voltage (Voc) and hence provides the higher PCE. The work opens up the possibility of using metal nitrides, instead of metal oxides, as carrier‐selective contacts or electron transport layers for photovoltaic devices.

  13. Electronic band structure, optical, dynamical and thermodynamic properties of cesium chloride (CsCl from first-principles

    Directory of Open Access Journals (Sweden)

    Bingol Suat

    2015-01-01

    Full Text Available The geometric structural optimization, electronic band structure, total density of states for valence electrons, density of states for phonons, optical, dynamical, and thermodynamical features of cesium chloride have been investigated by linearized augmented plane wave method using the density functional theory under the generalized gradient approximation. Ground state properties of cesium chloride are studied. The calculated ground state properties are consistent with experimental results. Calculated band structure indicates that the cesium chloride structure has an indirect band gap value of 5.46 eV and is an insulator. From the obtained phonon spectra, the cesium chloride structure is dynamically stable along the various directions in the Brillouin zone. Temperature dependent thermodynamic properties are studied using the harmonic approximation model.

  14. Inter-band B(E2) transitions strengths in 160-170Dy nuclei

    International Nuclear Information System (INIS)

    Vargas, Carlos E; Lerma, Sergio; Velázquez, Víctor

    2015-01-01

    The rare earth region of the nuclear landscape is characterized by a large collectivity observed. The microscopic studies are difficult to perform in the region due to the enormous size of the valence spaces. The use of symmetries based models avoids that problem, because the symmetry allows to choose the most relevant degrees of freedom for the system under consideration. We present theoretical results for electromagnetic properties in 160-168 Dy isotopes employing the pseudo-SU(3) model. In particular, we study the B(E2) inter-band transition strengths between the ground state, γ and, β-bands. The model succesfully describes in a systematic way rotational features in these nuclei and allows to extrapolate toward the midshell nucleus 170 Dy

  15. Valence band photoemission from in-situ grown GaAs(100)-c(4 x 4)

    Czech Academy of Sciences Publication Activity Database

    Jiříček, Petr; Cukr, Miroslav; Bartoš, Igor; Adell, M.; Strasser, T.; Schattke, W.

    2006-01-01

    Roč. 56, č. 1 (2006), s. 21-26 ISSN 0011-4626. [Symposium on Surface Physics /10./. Praha, 11.07.2005-15.07.2005] R&D Projects: GA ČR(CZ) GA202/04/0994 Institutional research plan: CEZ:AV0Z10100521 Keywords : GaAs(100)-c(4X4) * surface states * band structure * structure plot Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.568, year: 2006

  16. W-Band Sheet Beam Klystron Design

    International Nuclear Information System (INIS)

    Scheitrum, G.; Caryotakis, G.; Burke, A.; Jensen, A.; Jongewaard, E.; Krasnykh, A.; Neubauer, M.; Phillips, R.; Rauenbuehler, K.

    2011-01-01

    Sheet beam devices provide important advantages for very high power, narrow bandwidth RF sources like accelerator klystrons (1). Reduced current density and increased surface area result in increased power capabi1ity, reduced magnetic fields for focusing and reduced cathode loading. These advantages are offset by increased complexity, beam formation and transport issues and potential for mode competition in the ovennoded cavities and drift tube. This paper will describe the design issues encountered in developing a 100 kW peak and 2 kW average power sheet beam k1ystron at W-band including beam formation, beam transport, circuit design, circuit fabrication and mode competition.

  17. Channel estimation in DFT-based offset-QAM OFDM systems.

    Science.gov (United States)

    Zhao, Jian

    2014-10-20

    Offset quadrature amplitude modulation (offset-QAM) orthogonal frequency division multiplexing (OFDM) exhibits enhanced net data rates compared to conventional OFDM, and reduced complexity compared to Nyquist FDM (N-FDM). However, channel estimation in discrete-Fourier-transform (DFT) based offset-QAM OFDM is different from that in conventional OFDM and requires particular study. In this paper, we derive a closed-form expression for the demultiplexed signal in DFT-based offset-QAM systems and show that although the residual crosstalk is orthogonal to the decoded signal, its existence degrades the channel estimation performance when the conventional least-square method is applied. We propose and investigate four channel estimation algorithms for offset-QAM OFDM that vary in terms of performance, complexity, and tolerance to system parameters. It is theoretically and experimentally shown that simple channel estimation can be realized in offset-QAM OFDM with the achieved performance close to the theoretical limit. This, together with the existing advantages over conventional OFDM and N-FDM, makes this technology very promising for optical communication systems.

  18. Sample Adaptive Offset Optimization in HEVC

    Directory of Open Access Journals (Sweden)

    Yang Zhang

    2014-11-01

    Full Text Available As the next generation of video coding standard, High Efficiency Video Coding (HEVC adopted many useful tools to improve coding efficiency. Sample Adaptive Offset (SAO, is a technique to reduce sample distortion by providing offsets to pixels in in-loop filter. In SAO, pixels in LCU are classified into several categories, then categories and offsets are given based on Rate-Distortion Optimization (RDO of reconstructed pixels in a Largest Coding Unit (LCU. Pixels in a LCU are operated by the same SAO process, however, transform and inverse transform makes the distortion of pixels in Transform Unit (TU edge larger than the distortion inside TU even after deblocking filtering (DF and SAO. And the categories of SAO can also be refined, since it is not proper for many cases. This paper proposed a TU edge offset mode and a category refinement for SAO in HEVC. Experimental results shows that those two kinds of optimization gets -0.13 and -0.2 gain respectively compared with the SAO in HEVC. The proposed algorithm which using the two kinds of optimization gets -0.23 gain on BD-rate compared with the SAO in HEVC which is a 47 % increase with nearly no increase on coding time.

  19. NEVER forget: negative emotional valence enhances recapitulation.

    Science.gov (United States)

    Bowen, Holly J; Kark, Sarah M; Kensinger, Elizabeth A

    2017-07-10

    A hallmark feature of episodic memory is that of "mental time travel," whereby an individual feels they have returned to a prior moment in time. Cognitive and behavioral neuroscience methods have revealed a neurobiological counterpart: Successful retrieval often is associated with reactivation of a prior brain state. We review the emerging literature on memory reactivation and recapitulation, and we describe evidence for the effects of emotion on these processes. Based on this review, we propose a new model: Negative Emotional Valence Enhances Recapitulation (NEVER). This model diverges from existing models of emotional memory in three key ways. First, it underscores the effects of emotion during retrieval. Second, it stresses the importance of sensory processing to emotional memory. Third, it emphasizes how emotional valence - whether an event is negative or positive - affects the way that information is remembered. The model specifically proposes that, as compared to positive events, negative events both trigger increased encoding of sensory detail and elicit a closer resemblance between the sensory encoding signature and the sensory retrieval signature. The model also proposes that negative valence enhances the reactivation and storage of sensory details over offline periods, leading to a greater divergence between the sensory recapitulation of negative and positive memories over time. Importantly, the model proposes that these valence-based differences occur even when events are equated for arousal, thus rendering an exclusively arousal-based theory of emotional memory insufficient. We conclude by discussing implications of the model and suggesting directions for future research to test the tenets of the model.

  20. Dynamics of Impurity and Valence Bands in Ga1-xMnxAs Within the Dynamical Mean-Field Approximation

    International Nuclear Information System (INIS)

    Majidi, M.A.; Moreno, Juana; Jarrell, Mark; Fishman, Randy Scott; Aryanpour, K.A.

    2006-01-01

    We calculate the density-of-states and the spectral function of Ga 1-x Mn x As within the dynamical mean-field approximation. Our model includes the competing effects of the strong spin-orbit coupling on the J=3/2 GaAs hole bands and the exchange interaction between the magnetic ions and the itinerant holes. We study the quasiparticle and impurity bands in the paramagnetic and ferromagnetic phases for different values of impurity-hole coupling J c at a Mn doping of x=0.05. By analyzing the anisotropic angular distribution of the impurity band carriers at T=0, we conclude that the carrier polarization is optimal when the carriers move along the direction parallel to the average magnetization.

  1. Preparation and properties of radio-frequency-sputtered half-Heusler films for use in solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Kieven, D., E-mail: david.kieven@helmholtz-berlin.d [Helmholtz-Zentrum fuer Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Grimm, A. [Helmholtz-Zentrum fuer Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Beleanu, A.; Blum, C.G.F. [Johannes Gutenberg Universitaet, Institut fuer Anorganische Chemie und Analytische Chemie, Staudingerweg 9, 55128 Mainz (Germany); Schmidt, J. [Fraunhofer Institut Fertigungstechnik Materialforschung IFAM, Winterbergstrasse 28, 01277 Dresden (Germany); Rissom, T.; Lauermann, I. [Helmholtz-Zentrum fuer Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Gruhn, T.; Felser, C. [Johannes Gutenberg Universitaet, Institut fuer Anorganische Chemie und Analytische Chemie, Staudingerweg 9, 55128 Mainz (Germany); Klenk, R. [Helmholtz-Zentrum fuer Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin (Germany)

    2011-01-03

    The class of half-Heusler compounds opens possibilities to find alternatives for II-VI or III-V compound semiconductors. We aim to find suitable substitutes for the cadmium sulphide buffer layer in chalcopyrite-based thin film solar cells, where the buffer layer is located between the p-type chalcopyrite absorber and an n-type transparent window layer. We report here the preparation of radio-frequency-sputtered lithium copper sulphide 'LiCuS' and lithium zinc phosphide 'LiZnP' films. The optical analysis of these films revealed band gaps between 1.8 and 2.5 eV, respectively. Chemical properties of the film surface and both interfaces between the film and a Cu(In,Ga)Se{sub 2} layer and between the film and an (Zn,Mg)O layer were investigated by in-situ photoelectron spectroscopy. The valence band offsets to the Cu(In,Ga)Se{sub 2} layer were estimated to be (0.4 {+-} 0.1) eV for 'LiCuS'/Cu(In,Ga)Se{sub 2} and (0.5 {+-} 0.8) eV for 'LiZnP'/Cu(In,Ga)Se{sub 2}. This leads to positive conduction band offsets of > 1 eV. These rather large offsets are not compatible with efficient solar cell devices. Under atmospheric conditions 'LiCuS' and 'LiZnP' films show rapid decomposition.

  2. Electronic structure study of wide band gap magnetic semiconductor (La{sub 0.6}Pr{sub 0.4}){sub 0.65}Ca{sub 0.35}MnO{sub 3} nanocrystals in paramagnetic and ferromagnetic phases

    Energy Technology Data Exchange (ETDEWEB)

    Dwivedi, G. D.; Chou, H.; Yang, K. S.; Jhong, D. J.; Chan, W. L. [Department of Physics, National Sun Yat-sen University, Kaohsiung 80424, Taiwan (China); Joshi, Amish G. [CSIR-National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110012 (India); Kumar, Shiv; Ghosh, A. K. [Department of Physics, Banaras Hindu University, Varanasi 221005 (India); Chatterjee, Sandip, E-mail: schatterji.app@iitbhu.ac.in [Department of Physics, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005 (India)

    2016-04-25

    X-ray circular magnetic dichroism (XMCD), X-ray photoemission spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) techniques were used to study the electronic structure of nanocrystalline (La{sub 0.6}Pr{sub 0.4}){sub 0.65}Ca{sub 0.35}MnO{sub 3} near Fermi-level. XMCD results indicate that Mn{sup 3+} and Mn{sup 4+} spins are aligned parallel to each other at 20 K. The low M-H hysteresis curve measured at 5 K confirms ferromagnetic ordering in the (La{sub 0.6}Pr{sub 0.4}){sub 0.65}Ca{sub 0.35}MnO{sub 3} system. The low temperature valence band XPS indicates that coupling between Mn3d and O2p is enhanced and the electronic states near Fermi-level have been suppressed below T{sub C}. The valence band UPS also confirms the suppression of electronic states near Fermi-level below Curie temperature. UPS near Fermi-edge shows that the electronic states are almost absent below 0.5 eV (at 300 K) and 1 eV (at 115 K). This absence clearly demonstrates the existence of a wide band-gap in the system since, for hole-doped semiconductors, the Fermi-level resides just above the valence band maximum.

  3. Human Amygdala Tracks a Feature-Based Valence Signal Embedded within the Facial Expression of Surprise.

    Science.gov (United States)

    Kim, M Justin; Mattek, Alison M; Bennett, Randi H; Solomon, Kimberly M; Shin, Jin; Whalen, Paul J

    2017-09-27

    Human amygdala function has been traditionally associated with processing the affective valence (negative vs positive) of an emotionally charged event, especially those that signal fear or threat. However, this account of human amygdala function can be explained by alternative views, which posit that the amygdala might be tuned to either (1) general emotional arousal (activation vs deactivation) or (2) specific emotion categories (fear vs happy). Delineating the pure effects of valence independent of arousal or emotion category is a challenging task, given that these variables naturally covary under many circumstances. To circumvent this issue and test the sensitivity of the human amygdala to valence values specifically, we measured the dimension of valence within the single facial expression category of surprise. Given the inherent valence ambiguity of this category, we show that surprised expression exemplars are attributed valence and arousal values that are uniquely and naturally uncorrelated. We then present fMRI data from both sexes, showing that the amygdala tracks these consensus valence values. Finally, we provide evidence that these valence values are linked to specific visual features of the mouth region, isolating the signal by which the amygdala detects this valence information. SIGNIFICANCE STATEMENT There is an open question as to whether human amygdala function tracks the valence value of cues in the environment, as opposed to either a more general emotional arousal value or a more specific emotion category distinction. Here, we demonstrate the utility of surprised facial expressions because exemplars within this emotion category take on valence values spanning the dimension of bipolar valence (positive to negative) at a consistent level of emotional arousal. Functional neuroimaging data showed that amygdala responses tracked the valence of surprised facial expressions, unconfounded by arousal. Furthermore, a machine learning classifier identified

  4. Effects of valence and divided attention on cognitive reappraisal processes.

    Science.gov (United States)

    Morris, John A; Leclerc, Christina M; Kensinger, Elizabeth A

    2014-12-01

    Numerous studies have investigated the neural substrates supporting cognitive reappraisal, identifying the importance of cognitive control processes implemented by prefrontal cortex (PFC). This study examined how valence and attention affect the processes used for cognitive reappraisal by asking participants to passively view or to cognitively reappraise positive and negative images with full or divided attention. When participants simply viewed these images, results revealed few effects of valence or attention. However, when participants engaged in reappraisal, there was a robust effect of valence, with the reappraisal of negative relative to positive images associated with more widespread activation, including within regions of medial and lateral PFC. There also was an effect of attention, with more lateral PFC recruitment when regulating with full attention and more medial PFC recruitment when regulating with divided attention. Within two regions of medial PFC and one region of ventrolateral PFC, there was an interaction between valence and attention: in these regions, divided attention reduced activity during reappraisal of positive but not negative images. Critically, participants continued to report reappraisal success even during the Divided Attention condition. These results suggest multiple routes to successful cognitive reappraisal, depending upon image valence and the availability of attentional resources. © The Author (2014). Published by Oxford University Press. For Permissions, please email: journals.permissions@oup.com.

  5. Effects of valence and divided attention on cognitive reappraisal processes

    Science.gov (United States)

    Leclerc, Christina M.; Kensinger, Elizabeth A.

    2014-01-01

    Numerous studies have investigated the neural substrates supporting cognitive reappraisal, identifying the importance of cognitive control processes implemented by prefrontal cortex (PFC). This study examined how valence and attention affect the processes used for cognitive reappraisal by asking participants to passively view or to cognitively reappraise positive and negative images with full or divided attention. When participants simply viewed these images, results revealed few effects of valence or attention. However, when participants engaged in reappraisal, there was a robust effect of valence, with the reappraisal of negative relative to positive images associated with more widespread activation, including within regions of medial and lateral PFC. There also was an effect of attention, with more lateral PFC recruitment when regulating with full attention and more medial PFC recruitment when regulating with divided attention. Within two regions of medial PFC and one region of ventrolateral PFC, there was an interaction between valence and attention: in these regions, divided attention reduced activity during reappraisal of positive but not negative images. Critically, participants continued to report reappraisal success even during the Divided Attention condition. These results suggest multiple routes to successful cognitive reappraisal, depending upon image valence and the availability of attentional resources. PMID:24493837

  6. Handbook of Carbon Offset Programs. Trading Systems, Funds, Protocols and Standards

    Energy Technology Data Exchange (ETDEWEB)

    Kollmuss, Anja; Lazarus, Michael; Lee, Carrie; Polycarp, Clifford (SEI-US (United States)); LeFranc, Maurice (US EPA (United States))

    2010-03-15

    Greenhouse gas (GHG) offsets have long been promoted as an important element of a comprehensive climate policy approach. Offset programs can reduce the overall cost of achieving a given emission goal by enabling emission reductions to occur where costs are lower. Offsets have the potential to deliver sustainability co-benefits, through technology development and transfer. They can also develop human and institutional capacity for reducing emissions in sectors and locations not included in a cap and trade or a mandatory government policy. However, offsets can pose a risk to the environmental integrity of climate actions, especially if issues surrounding additionality, permanence, leakage, quantification and verification are not adequately addressed. The challenge is to design offset programs and policies that can maximize their potential benefits while minimizing their potential risks. This handbook provides a systematic and comprehensive review of existing offset programs. It looks are what offsets are, how offset mechanisms function, and the successes and pitfalls they have encountered. Coverage includes offset programs across the full swath of applications including mandatory and voluntary systems, government regulated and private markets, carbon offset funds, and accounting and reporting protocols such as the WBCSD/WRI GHG Protocol and ISO 14064. Learning from the successes and failures of these programs will be essential to crafting effective climate policy. A reference for regulators, policy makers, business leaders and NGOs concerned with the design and operation of GHG offset programs world-wide

  7. Relationship between acoustic voice onset and offset and selected instances of oscillatory onset and offset in young healthy males and females

    Science.gov (United States)

    Patel, Rita; Forrest, Karen; Hedges, Drew

    2016-01-01

    Objective To investigate the relationship between (1) onset of the acoustic signal and pre-phonatory phases associated with oscillatory onset and (2) offset of the acoustic signal with the post-phonatory events associated with oscillatory offset across vocally healthy adults. Subjects and Methods High-speed videoendoscopy was captured simultaneously with the acoustic signal during repeated production of /hi.hi.hi/ at typical pitch and loudness from 56 vocally healthy adults (age 20–42 years; 21 male, 35 female). The relationship between the acoustic sound pressure signal and oscillatory onset /offset events from the glottal area waveforms (GAW), were statistically investigated using a multivariate linear regression analysis. Results The onset of the acoustic signal (X1a) is a significant predictor of the onset of first oscillations (X1g) and onset of sustained oscillations (X2g). X1a as well as gender are significant predictors of the first instance of medial contact (X1.5g). The offset of the acoustic signal (X2a) is a significant predictor of the first instance of oscillatory offset (X3g), first instance of incomplete glottal closure (X3.5g), and cessation of vocal fold motion (X4g). Conclusions The acoustic signal onset is closely related to the first medial contact of the vocal folds but the latency between these events is longer for females compared to males. The offset of the acoustic signal occurs immediately after incomplete glottal adduction. The emerging normative group latencies between the onset/offset of the acoustic and the GAW from this study appear promising for future investigations. PMID:27769696

  8. Research on Stress Neutral Layer Offset in the Straightening Process

    Directory of Open Access Journals (Sweden)

    Hailian Gui

    2015-01-01

    Full Text Available The stress neutral layer offset is analyzed by theoretical and numerical calculation methods. In traditional straightening theory, the stress neutral layer was consistent with the geometric central layer. However, there is a phenomenon that the stress neutral layer has some offset with the geometric neutral layer. This offset is a very important factor for improving the precision of the straightening force. The formula of the stress neutral layer offset is obtained by a theoretical method and the change law is given by numerical calculation method. The neutral layer offset theory provides the theoretical basis for establishing the model of straightening force precisely.

  9. Determination of band structure parameters and the quasi-particle gap of CdSe quantum dots by cyclic voltammetry.

    Science.gov (United States)

    Inamdar, Shaukatali N; Ingole, Pravin P; Haram, Santosh K

    2008-12-01

    Band structure parameters such as the conduction band edge, the valence band edge and the quasi-particle gap of diffusing CdSe quantum dots (Q-dots) of various sizes were determined using cyclic voltammetry. These parameters are strongly dependent on the size of the Q-dots. The results obtained from voltammetric measurements are compared to spectroscopic and theoretical data. The fit obtained to the reported calculations based on the semi-empirical pseudopotential method (SEPM)-especially in the strong size-confinement region, is the best reported so far, according to our knowledge. For the smallest CdSe Q-dots, the difference between the quasi-particle gap and the optical band gap gives the electron-hole Coulombic interaction energy (J(e1,h1)). Interband states seen in the photoluminescence spectra were verified with cyclic voltammetry measurements.

  10. Evidence of ion intercalation mediated band structure modification and opto-ionic coupling in lithium niobite

    Energy Technology Data Exchange (ETDEWEB)

    Shank, Joshua C.; Tellekamp, M. Brooks; Doolittle, W. Alan, E-mail: alan.doolittle@ece.gatech.edu [Department of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States)

    2015-01-21

    The theoretically suggested band structure of the novel p-type semiconductor lithium niobite (LiNbO{sub 2}), the direct coupling of photons to ion motion, and optically induced band structure modifications are investigated by temperature dependent photoluminescence. LiNbO{sub 2} has previously been used as a memristor material but is shown here to be useful as a sensor owing to the electrical, optical, and chemical ease of lithium removal and insertion. Despite the high concentration of vacancies present in lithium niobite due to the intentional removal of lithium atoms, strong photoluminescence spectra are observed even at room temperature that experimentally confirm the suggested band structure implying transitions from a flat conduction band to a degenerate valence band. Removal of small amounts of lithium significantly modifies the photoluminescence spectra including additional larger than stoichiometric-band gap features. Sufficient removal of lithium results in the elimination of the photoluminescence response supporting the predicted transition from a direct to indirect band gap semiconductor. In addition, non-thermal coupling between the incident laser and lithium ions is observed and results in modulation of the electrical impedance.

  11. Memory effects of sleep, emotional valence, arousal and novelty in children.

    Science.gov (United States)

    Vermeulen, Marije C M; van der Heijden, Kristiaan B; Benjamins, Jeroen S; Swaab, Hanna; van Someren, Eus J W

    2017-06-01

    Effectiveness of memory consolidation is determined by multiple factors, including sleep after learning, emotional valence, arousal and novelty. Few studies investigated how the effect of sleep compares with (and interacts with) these other factors, of which virtually none are in children. The present study did so by repeated assessment of declarative memory in 386 children (45% boys) aged 9-11 years through an online word-pair task. Children were randomly assigned to either a morning or evening learning session of 30 unrelated word-pairs with positive, neutral or negative valenced cues and neutral targets. After immediately assessing baseline recognition, delayed recognition was recorded either 12 or 24 h later, resulting in four different assessment schedules. One week later, the procedure was repeated with exactly the same word-pairs to evaluate whether effects differed for relearning versus original novel learning. Mixed-effect logistic regression models were used to evaluate how the probability of correct recognition was affected by sleep, valence, arousal, novelty and their interactions. Both immediate and delayed recognition were worse for pairs with negatively valenced or less arousing cue words. Relearning improved immediate and delayed word-pair recognition. In contrast to these effects, sleep did not affect recognition, nor did sleep moderate the effects of arousal, valence and novelty. The findings suggest a robust inclination of children to specifically forget the pairing of words to negatively valenced cue words. In agreement with a recent meta-analysis, children seem to depend less on sleep for the consolidation of information than has been reported for adults, irrespective of the emotional valence, arousal and novelty of word-pairs. © 2017 European Sleep Research Society.

  12. Advantages of low beam energies in a TEM for valence EELS

    Science.gov (United States)

    Stöger-Pollach, M.; Pongratz, P.

    2010-02-01

    Since the availability of monochromators in transmission electron microscopes (TEMs), electron energy loss spectrometry (EELS) is widely used to determine band gaps and the dielectric properties of semiconductors on a nano-metre scale. Nevertheless, three physical effects hamper straightforward analysis: (a) relativistic energy losses, (b) the delocalization of the energy loss which is in the 10 nano-metreer range for valence losses, and (c) the presence of interface plasmons. When reducing the operation voltage of the TEM one can kill two birds with one stone: (a) the relativistic losses will disappear as soon as veinvestigated sample) and (b) the delocalization will decrease, because it also depends on the energy of the incident electron probe. The determination of the optical properties of quantum structures is discussed in the case of GaP/GaAs interface at 200 keV and 20 keV beam energy, respectively. Further, the influence of the delocalization of the energy loss signal is discussed theoretically and experimentally.

  13. Characteristics and structure of turbulent 3D offset jets

    International Nuclear Information System (INIS)

    Agelin-Chaab, M.; Tachie, M.F.

    2011-01-01

    Highlights: → We investigated three-dimensional turbulent offset jets using particle image velocimetry. → We examined the effects of offset height and Reynolds number on the structure of 3D offset jets. → Effects of Reynolds number and offset height on the decay and growth rates exist close to the exit. → This study provides additional insight and comprehensive data for validating numerical models. - Abstract: Three-dimensional turbulent offset jets were investigated using a particle image velocimetry technique. The measurements were performed at three different exit Reynolds numbers and for four offset heights. The results in the early region of flow development clearly show significant effects of Reynolds number and offset height on the decay of maximum mean velocity and growth of the shear layer. On the contrary, the decay and spread rates were found to be nearly independent of offset height at larger downstream distances. The decay rates of 1.18 ± 0.03 as well as the spread rates of 0.055 ± 0.001 and 0.250 ± 0.005 obtained, respectively, in the wall-normal and lateral directions fall in the range of values reported in previous studies. The locations of the maximum mean velocities increased nearly linearly with streamwise distance in the self-similar region. Analysis from two-point velocity correlations revealed substantially larger structures in the outer layer and self-similar region than in the inner layer and developing region. It was also observed that the hairpin vortices in the inner regions of the wall jets are inclined at angles of 11.2 o ± 0.6 o , which are in good agreement with reported values in boundary layer studies.

  14. Band shift of 2D transition-metal dichalcogenide alloys: size and composition effects

    Science.gov (United States)

    Zhao, Yipeng; Zhang, Zhe; Ouyang, Gang

    2018-04-01

    Band engineering of 2D transition-metal dichalcogenides (2D-TMDs) is a vital task for their applications in electronic and optoelectronic nanodevices. In this study, we investigate the joint effect from size and composition contributions on the band shift of 2D-TMD alloys in terms of atomic bond relaxation consideration. A theoretical model is proposed to pursue the underlying mechanism, which can connect the band offset with the atomic bonding identities in the 2D-TMD alloys. We reveal that the bandgap of 2D-TMD alloys presents a bowing shape owing to the size-dependent interaction among atoms and shows blue shift or red shift due to different intermixing of components. It is demonstrated that both size and composition can be performed as the useful methods to modulate the band shift, which suggests an effective way to realize the desirable properties of 2D-TMD alloys.

  15. Formation of Offset and Dual Active Galactic Nuclei

    Science.gov (United States)

    Barrows, Scott; Comerford, Julia M.; Greene, Jenny E.

    2018-06-01

    Galaxy mergers are effective mechanisms for triggering accretion onto supermassive black holes (SMBHs) and thereby powering active galactic nuclei (AGN). In the merger scenario, when the SMBH from only one galaxy is accreting we observe a spatially offset AGN, and when the SMBHs from both galaxies are accreting we observe a dual AGN. Understanding the merger conditions that lead to the formation of offset AGN versus dual AGN is fundamental to informing models of hierarchical SMBH growth and the physics leading to the accretion of matter onto SMBHs. However, while the role of galaxy mergers for AGN triggering has been well-studied, the efficiency with which these events trigger offset AGN versus dual AGN is currently unclear. One reason for this gap in knowledge can be attributed to the observational difficulties in distinguishing between offset and dual AGN since doing so requires high spatial resolution, especially in the small separation regime where merger-driven AGN triggering is most likely to occur. To overcome this hurdle, we have utilized the spatial resolution of the Chandra X-ray Observatory to develop a unique sample of AGN hosted by late-stage galaxy mergers. Moreover, we have recently acquired Hubble Space Telescope imaging for a subset of these systems to examine the role that their merger morphologies play in SMBH growth and the formation of offset and dual AGN. We find that offset AGN are predominately found in minor mergers, whereas dual AGN are usually hosted by major mergers and galaxies with large morphological asymmetries. Furthermore, in both offset and dual AGN, the rate of SMBH growth increases toward more major mergers and larger morphological asymmetries. These results are in agreement with numerical simulations predicting that merger morphology is a relevant parameter governing SMBH merger-driven growth, and these results are the first to observationally confirm these trends at small pair separations.

  16. Carbon offsets, reversal risk and US climate policy

    Directory of Open Access Journals (Sweden)

    Chen Yihsu

    2009-06-01

    Full Text Available Abstract Background One controversial issue in the larger cap-and-trade debate is the proper use and certification of carbon offsets related to changes in land management. Advocates of an expanded offset supply claim that inclusion of such activities would expand the scope of the program and lower overall compliance costs, while opponents claim that it would weaken the environmental integrity of the program by crediting activities that yield either nonexistent or merely temporary carbon sequestration benefits. Our study starts from the premise that offsets are neither perfect mitigation instruments nor useless "hot air." Results We show that offsets provide a useful cost containment function, even when there is some threat of reversal, by injecting additional "when-flexibility" into the system. This allows market participants to shift their reduction requirements to periods of lower cost, thereby facilitating attainment of the least-cost time path without jeopardizing the cumulative environmental integrity of the system. By accounting for market conditions in conjunction with reversal risk, we develop a simple offset valuation methodology, taking into account the two most important factors that typically lead offsets to be overvalued or undervalued. Conclusion The result of this paper is a quantitative "model rule" that could be included in future legislation or used as a basis for active management by a future "carbon fed" or other regulatory authority with jurisdiction over the US carbon market to actively manage allowance prices.

  17. Growth of amorphous Zn–Sn–O thin films by RF sputtering for buffer layers of CuInSe2 and SnS solar cells

    International Nuclear Information System (INIS)

    Chang, Shao-Wei; Ishikawa, Kaoru; Sugiyama, Mutsumi

    2015-01-01

    We propose using amorphous Zn–Sn–O (α-ZTO) deposited by RF sputtering as an alternative n-type buffer layer for Cu(In,Ga)Se 2 and SnS solar cells. The order of the carrier density, n, is increased from the order of 10 15 to 10 17 cm −1 as the Sn/(Sn + Zn) atomic ratio increases from 0.29 to 0.40. On the other hand, the order of n decreased from 10 17 to 10 11 cm −1 as the oxygen partial pressure increased from 0 to 10%. Further, for the α-ZTO film with the Sn/(Sn + Zn) atomic ratio at 0.38 and the oxygen partial pressure at 0%, valence band discontinuities of α-ZTO/CuInSe 2 and α-ZTO/SnS were determined using photoelectron yield spectroscopy measurements. The band discontinuities of each of these interfaces form a spike structure in the conduction band offset, which enables a high-performance solar cell to be obtained. - Highlights: • We propose using amorphous Zn–Sn–O as a n-type layer for Cu(In,Ga)Se 2 and SnS solar cells. • The carrier density was controlled by total and/or oxygen partial pressure during sputtering. • Valence band discontinuities of Zn–Sn–O/CuInSe 2 and Zn–Sn–O/SnS were determined. • The conduction band discontinuities of each of these interfaces form a spike structure

  18. Investigating Valence and Autonomy in Children's Relationships with Imaginary Companions

    Science.gov (United States)

    McInnis, Melissa A.; Pierucci, Jillian M.; Gilpin, Ansley Tullos

    2013-01-01

    Little research has explored valence and autonomy in children's imaginary relationships. In the present study, a new interview (modeled after an existing measure for real relationships) was designed to elicit descriptions of both positive and negative interactions with imaginary companions and to provide a measure of relationship valence and…

  19. Type I band alignment in GaAs{sub 81}Sb{sub 19}/GaAs core-shell nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Xu, T. [Institut d' Electronique, de Microélectronique et de Nanotechnologies (IEMN), CNRS, UMR 8520, Département ISEN, 41 bd Vauban, 59046 Lille Cedex (France); Key Laboratory of Advanced Display and System Application, Shanghai University, 149 Yanchang Road, Shanghai 200072 (China); Wei, M. J. [Key Laboratory of Advanced Display and System Application, Shanghai University, 149 Yanchang Road, Shanghai 200072 (China); Capiod, P.; Díaz Álvarez, A.; Han, X. L.; Troadec, D.; Nys, J. P.; Berthe, M.; Lefebvre, I.; Grandidier, B., E-mail: bruno.grandidier@isen.iemn.univ-lille1.fr [Institut d' Electronique, de Microélectronique et de Nanotechnologies (IEMN), CNRS, UMR 8520, Département ISEN, 41 bd Vauban, 59046 Lille Cedex (France); Patriarche, G. [CNRS-Laboratoire de Photonique et de Nanostructures (LPN), Route de Nozay, 91460 Marcoussis (France); Plissard, S. R. [Institut d' Electronique, de Microélectronique et de Nanotechnologies (IEMN), CNRS, UMR 8520, Département ISEN, 41 bd Vauban, 59046 Lille Cedex (France); CNRS-Laboratoire d' Analyse et d' Architecture des Systèmes (LAAS), Univ. de Toulouse, 7 Avenue du Colonel Roche, F-31400 Toulouse (France); Caroff, P. [Institut d' Electronique, de Microélectronique et de Nanotechnologies (IEMN), CNRS, UMR 8520, Département ISEN, 41 bd Vauban, 59046 Lille Cedex (France); Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, Australian Capital Territory 0200 (Australia); and others

    2015-09-14

    The composition and band gap of the shell that formed during the growth of axial GaAs/GaAs{sub 81}Sb{sub 19}/ GaAs heterostructure nanowires have been investigated by transmission electron microscopy combined with energy dispersion spectroscopy, scanning tunneling spectroscopy, and density functional theory calculations. On the GaAs{sub 81}Sb{sub 19} intermediate segment, the shell is found to be free of Sb (pure GaAs shell) and transparent to the tunneling electrons, despite the (110) biaxial strain that affects its band gap. As a result, a direct measurement of the core band gap allows the quantitative determination of the band offset between the GaAs{sub 81}Sb{sub 19} core and the GaAs shell and identifies it as a type I band alignment.

  20. Offset Implementations for Turkey’s International Defense Acquisitions

    Science.gov (United States)

    2008-12-01

    has been a source of confusion in the field of offsets and countertrade (Schmidt, 1989, p. 4) Compensatory trade agreements — or reciprocal trade...complementary policy instruments. Countertrade and offset terms have usually been overall terms to define and classify reciprocal trade agreements...motives and characteristics in nature. Author Grant T. Hammond classifies reciprocal trade as countertrade , offsets and barter — which involve all